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 $71.45   6.771%   $76.2879   $76.29   $76.30   $76.30  
  Purchase #2 $55.57   12.852%   $62.7119   $62.71   $62.70   $62.70  
  Purchase #3 $117.50   3.713%   $121.8628   $121.86   $121.85   $121.90  
  Purchase #4 $168.32   10.324%   $185.6974   $185.70   $185.70   $185.70  
  Purchase #5 $133.98   11.195%   $148.9791   $148.98   $149.00   $149.00  
  Purchase #6 $5.92   11.204%   $6.5833   $6.58   $6.60   $6.60  
  Purchase #7 $72.42   13.703%   $82.3437   $82.34   $82.35   $82.30  
  7 purchase totals = $625.16       $684.4661   $684.46   $684.50   $684.50