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 $222.26   12.490%   $250.0203   $250.02   $250.00   $250.00  
  Purchase #2 $67.62   8.204%   $73.1675   $73.17   $73.15   $73.20  
  Purchase #3 $131.51   10.518%   $145.3422   $145.34   $145.35   $145.30  
  Purchase #4 $6.89   7.200%   $7.3861   $7.39   $7.40   $7.40  
  Purchase #5 $143.39   8.516%   $155.6011   $155.60   $155.60   $155.60  
  Purchase #6 $161.66   5.165%   $170.0097   $170.01   $170.00   $170.00  
  Purchase #7 $236.93   8.760%   $257.6851   $257.69   $257.70   $257.70  
  7 purchase totals = $970.26       $1,059.2120   $1,059.22   $1,059.20   $1,059.20