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 $57.84   12.634%   $65.1475   $65.15   $65.15   $65.10  
  Purchase #2 $183.98   3.490%   $190.4009   $190.40   $190.40   $190.40  
  Purchase #3 $158.92   10.705%   $175.9324   $175.93   $175.95   $175.90  
  Purchase #4 $98.81   7.488%   $106.2089   $106.21   $106.20   $106.20  
  Purchase #5 $232.68   6.451%   $247.6902   $247.69   $247.70   $247.70  
  Purchase #6 $247.32   11.576%   $275.9498   $275.95   $275.95   $275.90  
  Purchase #7 $56.79   4.360%   $59.266   $59.27   $59.25   $59.30  
  7 purchase totals = $1,036.34       $1,120.5957   $1,120.60   $1,120.60   $1,120.50