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 $244.96   10.847%   $271.5308   $271.53   $271.55   $271.50  
  Purchase #2 $172.49   6.203%   $183.1896   $183.19   $183.20   $183.20  
  Purchase #3 $32.35   11.523%   $36.0777   $36.08   $36.10   $36.10  
  Purchase #4 $68.67   6.616%   $73.2132   $73.21   $73.20   $73.20  
  Purchase #5 $167.48   4.491%   $175.0015   $175.00   $175.00   $175.00  
  Purchase #6 $127.54   4.192%   $132.8865   $132.89   $132.90   $132.90  
  Purchase #7 $209.86   6.810%   $224.1515   $224.15   $224.15   $224.20  
  7 purchase totals = $1,023.35       $1,096.0508   $1,096.05   $1,096.10   $1,096.10