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 $209.92   11.111%   $233.2442   $233.24   $233.25   $233.20  
  Purchase #2 $171.95   7.578%   $184.9804   $184.98   $185.00   $185.00  
  Purchase #3 $43.60   13.436%   $49.4581   $49.46   $49.45   $49.50  
  Purchase #4 $123.52   10.377%   $136.3377   $136.34   $136.35   $136.30  
  Purchase #5 $130.51   10.874%   $144.7017   $144.70   $144.70   $144.70  
  Purchase #6 $207.69   13.811%   $236.3741   $236.37   $236.35   $236.40  
  Purchase #7 $106.35   8.423%   $115.3079   $115.31   $115.30   $115.30  
  7 purchase totals = $993.54       $1,100.4041   $1,100.40   $1,100.40   $1,100.40