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 $62.96   12.277%   $70.6896   $70.69   $70.70   $70.70  
  Purchase #2 $58.70   10.164%   $64.6663   $64.67   $64.65   $64.70  
  Purchase #3 $44.82   4.423%   $46.8024   $46.80   $46.80   $46.80  
  Purchase #4 $126.83   4.292%   $132.2735   $132.27   $132.25   $132.30  
  Purchase #5 $192.33   8.199%   $208.0991   $208.10   $208.10   $208.10  
  Purchase #6 $235.99   11.413%   $262.9235   $262.92   $262.90   $262.90  
  Purchase #7 $184.38   4.249%   $192.2143   $192.21   $192.20   $192.20  
  7 purchase totals = $906.01       $977.6687   $977.66   $977.60   $977.70