Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $167.61   12.627%   $188.7741   $188.77   $188.75   $188.80  
  Purchase #2 $248.34   13.833%   $282.6929   $282.69   $282.70   $282.70  
  Purchase #3 $101.32   7.301%   $108.7174   $108.72   $108.70   $108.70  
  Purchase #4 $238.95   10.234%   $263.4041   $263.40   $263.40   $263.40  
  Purchase #5 $124.78   12.689%   $140.6133   $140.61   $140.60   $140.60  
  Purchase #6 $164.29   6.232%   $174.5286   $174.53   $174.55   $174.50  
  Purchase #7 $178.42   9.645%   $195.6286   $195.63   $195.65   $195.60  
  7 purchase totals = $1,223.71       $1,354.3590   $1,354.35   $1,354.35   $1,354.30