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 $23.95   4.174%   $24.9497   $24.95   $24.95   $24.90  
  Purchase #2 $122.31   13.580%   $138.9197   $138.92   $138.90   $138.90  
  Purchase #3 $212.44   3.197%   $219.2317   $219.23   $219.25   $219.20  
  Purchase #4 $90.69   4.273%   $94.5652   $94.57   $94.55   $94.60  
  Purchase #5 $164.72   3.307%   $170.1673   $170.17   $170.15   $170.20  
  Purchase #6 $62.46   11.828%   $69.8478   $69.85   $69.85   $69.80  
  Purchase #7 $250.56   3.249%   $258.7007   $258.70   $258.70   $258.70  
  7 purchase totals = $927.13       $976.3821   $976.39   $976.35   $976.30