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 $105.79   7.172%   $113.3773   $113.38   $113.40   $113.40  
  Purchase #2 $190.25   13.522%   $215.9756   $215.98   $216.00   $216.00  
  Purchase #3 $225.46   8.741%   $245.1675   $245.17   $245.15   $245.20  
  Purchase #4 $60.43   13.819%   $68.7808   $68.78   $68.80   $68.80  
  Purchase #5 $26.39   12.756%   $29.7563   $29.76   $29.75   $29.80  
  Purchase #6 $209.76   12.354%   $235.6738   $235.67   $235.65   $235.70  
  Purchase #7 $39.68   4.574%   $41.495   $41.50   $41.50   $41.50  
  7 purchase totals = $857.76       $950.2263   $950.24   $950.25   $950.40