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 $85.92   6.601%   $91.5916   $91.59   $91.60   $91.60  
  Purchase #2 $242.42   13.521%   $275.1976   $275.20   $275.20   $275.20  
  Purchase #3 $217.97   7.701%   $234.7559   $234.76   $234.75   $234.80  
  Purchase #4 $36.71   13.454%   $41.649   $41.65   $41.65   $41.60  
  Purchase #5 $232.28   9.725%   $254.8692   $254.87   $254.85   $254.90  
  Purchase #6 $239.86   3.109%   $247.3172   $247.32   $247.30   $247.30  
  Purchase #7 $187.59   11.636%   $209.418   $209.42   $209.40   $209.40  
  7 purchase totals = $1,242.75       $1,354.7985   $1,354.81   $1,354.75   $1,354.80