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 $24.38   5.594%   $25.7438   $25.74   $25.75   $25.70  
  Purchase #2 $136.25   8.785%   $148.2196   $148.22   $148.20   $148.20  
  Purchase #3 $110.38   10.387%   $121.8452   $121.85   $121.85   $121.80  
  Purchase #4 $65.93   4.181%   $68.6865   $68.69   $68.70   $68.70  
  Purchase #5 $214.72   3.793%   $222.8643   $222.86   $222.85   $222.90  
  Purchase #6 $203.25   11.528%   $226.6807   $226.68   $226.70   $226.70  
  Purchase #7 $206.36   7.178%   $221.1725   $221.17   $221.15   $221.20  
  7 purchase totals = $961.27       $1,035.2126   $1,035.21   $1,035.20   $1,035.20