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 $51.53   4.360%   $53.7767   $53.78   $53.80   $53.80  
  Purchase #2 $118.65   11.445%   $132.2295   $132.23   $132.25   $132.20  
  Purchase #3 $225.81   7.172%   $242.0051   $242.01   $242.00   $242.00  
  Purchase #4 $138.98   8.761%   $151.156   $151.16   $151.15   $151.20  
  Purchase #5 $129.93   10.583%   $143.6805   $143.68   $143.70   $143.70  
  Purchase #6 $226.90   11.591%   $253.2   $253.20   $253.20   $253.20  
  Purchase #7 $50.64   12.688%   $57.0652   $57.07   $57.05   $57.10  
  7 purchase totals = $942.44       $1,033.1130   $1,033.13   $1,033.15   $1,033.20