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 $224.38   12.574%   $252.5935   $252.59   $252.60   $252.60  
  Purchase #2 $55.81   9.810%   $61.285   $61.29   $61.30   $61.30  
  Purchase #3 $163.75   6.485%   $174.3692   $174.37   $174.35   $174.40  
  Purchase #4 $106.93   9.304%   $116.8788   $116.88   $116.90   $116.90  
  Purchase #5 $148.51   12.664%   $167.3173   $167.32   $167.30   $167.30  
  Purchase #6 $186.44   12.456%   $209.663   $209.66   $209.65   $209.70  
  Purchase #7 $166.78   12.646%   $187.871   $187.87   $187.85   $187.90  
  7 purchase totals = $1,052.60       $1,169.9778   $1,169.98   $1,169.95   $1,170.10