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 $61.96   6.559%   $66.024   $66.02   $66.00   $66.00  
  Purchase #2 $81.40   10.518%   $89.9617   $89.96   $89.95   $90.00  
  Purchase #3 $229.53   9.174%   $250.5871   $250.59   $250.60   $250.60  
  Purchase #4 $166.45   9.120%   $181.6302   $181.63   $181.65   $181.60  
  Purchase #5 $188.92   11.172%   $210.0261   $210.03   $210.05   $210.00  
  Purchase #6 $193.61   12.153%   $217.1394   $217.14   $217.15   $217.10  
  Purchase #7 $178.78   11.478%   $199.3004   $199.30   $199.30   $199.30  
  7 purchase totals = $1,100.65       $1,214.6689   $1,214.67   $1,214.70   $1,214.60