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 $23.67   6.843%   $25.2897   $25.29   $25.30   $25.30  
  Purchase #2 $140.97   13.781%   $160.3971   $160.40   $160.40   $160.40  
  Purchase #3 $116.96   5.613%   $123.525   $123.53   $123.55   $123.50  
  Purchase #4 $67.53   12.816%   $76.1846   $76.18   $76.20   $76.20  
  Purchase #5 $153.31   5.225%   $161.3204   $161.32   $161.30   $161.30  
  Purchase #6 $63.65   3.847%   $66.0986   $66.10   $66.10   $66.10  
  Purchase #7 $227.42   12.507%   $255.8634   $255.86   $255.85   $255.90  
  7 purchase totals = $793.51       $868.6788   $868.68   $868.70   $868.70