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 $149.47   11.562%   $166.7517   $166.75   $166.75   $166.80  
  Purchase #2 $147.26   8.397%   $159.6254   $159.63   $159.65   $159.60  
  Purchase #3 $146.95   11.606%   $164.005   $164.01   $164.00   $164.00  
  Purchase #4 $237.96   11.386%   $265.0541   $265.05   $265.05   $265.10  
  Purchase #5 $98.42   8.263%   $106.5524   $106.55   $106.55   $106.60  
  Purchase #6 $18.45   4.642%   $19.3064   $19.31   $19.30   $19.30  
  Purchase #7 $55.73   8.874%   $60.6755   $60.68   $60.70   $60.70  
  7 purchase totals = $854.24       $941.9705   $941.98   $942.00   $942.10