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 $54.67   12.443%   $61.4726   $61.47   $61.45   $61.50  
  Purchase #2 $221.83   3.508%   $229.6118   $229.61   $229.60   $229.60  
  Purchase #3 $107.66   10.410%   $118.8674   $118.87   $118.85   $118.90  
  Purchase #4 $26.61   11.361%   $29.6332   $29.63   $29.65   $29.60  
  Purchase #5 $242.81   13.592%   $275.8127   $275.81   $275.80   $275.80  
  Purchase #6 $173.56   12.140%   $194.6302   $194.63   $194.65   $194.60  
  Purchase #7 $116.88   7.649%   $125.8202   $125.82   $125.80   $125.80  
  7 purchase totals = $944.02       $1,035.8481   $1,035.84   $1,035.80   $1,035.80