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 $66.74   5.214%   $70.2198   $70.22   $70.20   $70.20  
  Purchase #2 $231.86   10.603%   $256.4441   $256.44   $256.45   $256.40  
  Purchase #3 $57.78   11.687%   $64.5327   $64.53   $64.55   $64.50  
  Purchase #4 $109.38   4.606%   $114.418   $114.42   $114.40   $114.40  
  Purchase #5 $223.29   13.831%   $254.1732   $254.17   $254.15   $254.20  
  Purchase #6 $41.70   5.563%   $44.0198   $44.02   $44.00   $44.00  
  Purchase #7 $58.34   10.555%   $64.4978   $64.50   $64.50   $64.50  
  7 purchase totals = $789.09       $868.3054   $868.30   $868.25   $868.20