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 $90.36   3.266%   $93.3112   $93.31   $93.30   $93.30  
  Purchase #2 $24.66   4.761%   $25.8341   $25.83   $25.85   $25.80  
  Purchase #3 $223.34   7.467%   $240.0168   $240.02   $240.00   $240.00  
  Purchase #4 $138.29   9.164%   $150.9629   $150.96   $150.95   $151.00  
  Purchase #5 $148.96   6.466%   $158.5918   $158.59   $158.60   $158.60  
  Purchase #6 $175.59   12.332%   $197.2438   $197.24   $197.25   $197.20  
  Purchase #7 $70.87   10.649%   $78.4169   $78.42   $78.40   $78.40  
  7 purchase totals = $872.07       $944.3775   $944.37   $944.35   $944.30