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 $62.35   6.620%   $66.4776   $66.48   $66.50   $66.50  
  Purchase #2 $84.38   10.603%   $93.3268   $93.33   $93.35   $93.30  
  Purchase #3 $217.31   10.332%   $239.7625   $239.76   $239.75   $239.80  
  Purchase #4 $234.82   8.634%   $255.0944   $255.09   $255.10   $255.10  
  Purchase #5 $65.79   9.358%   $71.9466   $71.95   $71.95   $71.90  
  Purchase #6 $138.27   9.711%   $151.6974   $151.70   $151.70   $151.70  
  Purchase #7 $219.32   13.360%   $248.6212   $248.62   $248.60   $248.60  
  7 purchase totals = $1,022.24       $1,126.9265   $1,126.93   $1,126.95   $1,126.90