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 $119.63   10.618%   $132.3323   $132.33   $132.35   $132.30  
  Purchase #2 $62.65   3.695%   $64.9649   $64.96   $64.95   $65.00  
  Purchase #3 $23.92   3.372%   $24.7266   $24.73   $24.75   $24.70  
  Purchase #4 $38.41   5.858%   $40.6601   $40.66   $40.65   $40.70  
  Purchase #5 $70.67   13.419%   $80.1532   $80.15   $80.15   $80.20  
  Purchase #6 $106.38   4.690%   $111.3692   $111.37   $111.35   $111.40  
  Purchase #7 $143.81   3.179%   $148.3817   $148.38   $148.40   $148.40  
  7 purchase totals = $565.47       $602.5880   $602.58   $602.60   $602.70