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 $98.81   5.776%   $104.5173   $104.52   $104.50   $104.50  
  Purchase #2 $131.86   10.843%   $146.1576   $146.16   $146.15   $146.20  
  Purchase #3 $220.84   13.292%   $250.1941   $250.19   $250.20   $250.20  
  Purchase #4 $36.57   10.751%   $40.5016   $40.50   $40.50   $40.50  
  Purchase #5 $183.31   9.269%   $200.301   $200.30   $200.30   $200.30  
  Purchase #6 $22.80   5.322%   $24.0134   $24.01   $24.00   $24.00  
  Purchase #7 $169.58   11.107%   $188.4153   $188.42   $188.40   $188.40  
  7 purchase totals = $863.77       $954.1003   $954.10   $954.05   $954.10