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 $184.88   10.795%   $204.8378   $204.84   $204.85   $204.80  
  Purchase #2 $216.58   4.812%   $227.0018   $227.00   $227.00   $227.00  
  Purchase #3 $78.66   5.705%   $83.1476   $83.15   $83.15   $83.10  
  Purchase #4 $63.28   12.161%   $70.9755   $70.98   $71.00   $71.00  
  Purchase #5 $66.92   8.349%   $72.5072   $72.51   $72.50   $72.50  
  Purchase #6 $221.51   3.352%   $228.935   $228.94   $228.95   $228.90  
  Purchase #7 $81.35   9.203%   $88.8366   $88.84   $88.85   $88.80  
  7 purchase totals = $913.18       $976.2415   $976.26   $976.30   $976.10