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 $91.88   7.867%   $99.1082   $99.11   $99.10   $99.10  
  Purchase #2 $104.47   8.751%   $113.6122   $113.61   $113.60   $113.60  
  Purchase #3 $227.56   5.775%   $240.7016   $240.70   $240.70   $240.70  
  Purchase #4 $211.87   11.373%   $235.966   $235.97   $235.95   $236.00  
  Purchase #5 $66.40   8.849%   $72.2757   $72.28   $72.30   $72.30  
  Purchase #6 $55.98   6.153%   $59.4244   $59.42   $59.40   $59.40  
  Purchase #7 $116.60   5.163%   $122.6201   $122.62   $122.60   $122.60  
  7 purchase totals = $874.76       $943.7082   $943.71   $943.65   $943.70