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 $205.34   8.124%   $222.0218   $222.02   $222.00   $222.00  
  Purchase #2 $130.49   4.168%   $135.9288   $135.93   $135.95   $135.90  
  Purchase #3 $71.83   11.731%   $80.2564   $80.26   $80.25   $80.30  
  Purchase #4 $181.70   6.445%   $193.4106   $193.41   $193.40   $193.40  
  Purchase #5 $229.63   6.318%   $244.138   $244.14   $244.15   $244.10  
  Purchase #6 $162.75   3.120%   $167.8278   $167.83   $167.85   $167.80  
  Purchase #7 $148.60   12.354%   $166.958   $166.96   $166.95   $167.00  
  7 purchase totals = $1,130.34       $1,210.5414   $1,210.55   $1,210.55   $1,210.50