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 $118.31   11.658%   $132.1026   $132.10   $132.10   $132.10  
  Purchase #2 $234.80   13.129%   $265.6269   $265.63   $265.65   $265.60  
  Purchase #3 $45.94   10.356%   $50.6975   $50.70   $50.70   $50.70  
  Purchase #4 $233.41   12.521%   $262.6353   $262.64   $262.65   $262.60  
  Purchase #5 $106.88   9.781%   $117.3339   $117.33   $117.35   $117.30  
  Purchase #6 $163.48   10.209%   $180.1697   $180.17   $180.15   $180.20  
  Purchase #7 $248.44   7.777%   $267.7612   $267.76   $267.75   $267.80  
  7 purchase totals = $1,151.26       $1,276.3271   $1,276.33   $1,276.35   $1,276.30