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 $67.59   13.761%   $76.8911   $76.89   $76.90   $76.90  
  Purchase #2 $219.72   8.356%   $238.0798   $238.08   $238.10   $238.10  
  Purchase #3 $54.32   9.578%   $59.5228   $59.52   $59.50   $59.50  
  Purchase #4 $107.73   13.798%   $122.5946   $122.59   $122.60   $122.60  
  Purchase #5 $176.33   6.858%   $188.4227   $188.42   $188.40   $188.40  
  Purchase #6 $195.66   6.853%   $209.0686   $209.07   $209.05   $209.10  
  Purchase #7 $118.91   9.129%   $129.7653   $129.77   $129.75   $129.80  
  7 purchase totals = $940.26       $1,024.3449   $1,024.34   $1,024.30   $1,024.40