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 $9.32   10.859%   $10.3321   $10.33   $10.35   $10.30  
  Purchase #2 $70.80   11.313%   $78.8096   $78.81   $78.80   $78.80  
  Purchase #3 $22.85   10.237%   $25.1892   $25.19   $25.20   $25.20  
  Purchase #4 $12.56   4.141%   $13.0801   $13.08   $13.10   $13.10  
  Purchase #5 $218.76   4.669%   $228.9739   $228.97   $228.95   $229.00  
  Purchase #6 $150.57   5.699%   $159.151   $159.15   $159.15   $159.20  
  Purchase #7 $197.78   12.215%   $221.9388   $221.94   $221.95   $221.90  
  7 purchase totals = $682.64       $737.4747   $737.47   $737.50   $737.50