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 $211.92   8.141%   $229.1724   $229.17   $229.15   $229.20  
  Purchase #2 $125.48   7.863%   $135.3465   $135.35   $135.35   $135.30  
  Purchase #3 $173.98   3.556%   $180.1667   $180.17   $180.15   $180.20  
  Purchase #4 $191.51   7.845%   $206.534   $206.53   $206.55   $206.50  
  Purchase #5 $105.75   5.851%   $111.9374   $111.94   $111.95   $111.90  
  Purchase #6 $59.84   8.616%   $64.9958   $65.00   $65.00   $65.00  
  Purchase #7 $78.80   3.152%   $81.2838   $81.28   $81.30   $81.30  
  7 purchase totals = $947.28       $1,009.4366   $1,009.44   $1,009.45   $1,009.40