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 $83.76   12.621%   $94.3313   $94.33   $94.35   $94.30  
  Purchase #2 $201.78   9.355%   $220.6565   $220.66   $220.65   $220.70  
  Purchase #3 $173.59   7.627%   $186.8297   $186.83   $186.85   $186.80  
  Purchase #4 $172.58   6.448%   $183.708   $183.71   $183.70   $183.70  
  Purchase #5 $58.89   13.591%   $66.8937   $66.89   $66.90   $66.90  
  Purchase #6 $29.41   13.872%   $33.4898   $33.49   $33.50   $33.50  
  Purchase #7 $120.28   5.747%   $127.1925   $127.19   $127.20   $127.20  
  7 purchase totals = $840.29       $913.1015   $913.10   $913.15   $913.10