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 $196.92   3.331%   $203.4794   $203.48   $203.50   $203.50  
  Purchase #2 $51.45   8.605%   $55.8773   $55.88   $55.90   $55.90  
  Purchase #3 $168.34   7.292%   $180.6154   $180.62   $180.60   $180.60  
  Purchase #4 $172.53   6.749%   $184.174   $184.17   $184.15   $184.20  
  Purchase #5 $60.94   8.312%   $66.0053   $66.01   $66.00   $66.00  
  Purchase #6 $77.53   12.693%   $87.3709   $87.37   $87.35   $87.40  
  Purchase #7 $103.59   3.532%   $107.2488   $107.25   $107.25   $107.20  
  7 purchase totals = $831.30       $884.7711   $884.78   $884.75   $884.80