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 $61.65   9.631%   $67.5875   $67.59   $67.60   $67.60  
  Purchase #2 $124.77   6.135%   $132.4246   $132.42   $132.40   $132.40  
  Purchase #3 $154.53   4.209%   $161.0342   $161.03   $161.05   $161.00  
  Purchase #4 $37.65   10.560%   $41.6258   $41.63   $41.65   $41.60  
  Purchase #5 $213.39   13.809%   $242.857   $242.86   $242.85   $242.90  
  Purchase #6 $71.92   4.713%   $75.3096   $75.31   $75.30   $75.30  
  Purchase #7 $112.52   5.311%   $118.4959   $118.50   $118.50   $118.50  
  7 purchase totals = $776.43       $839.3346   $839.34   $839.35   $839.30