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 $66.51   12.353%   $74.726   $74.73   $74.75   $74.70  
  Purchase #2 $56.82   10.356%   $62.7043   $62.70   $62.70   $62.70  
  Purchase #3 $144.68   12.422%   $162.6521   $162.65   $162.65   $162.70  
  Purchase #4 $220.27   7.859%   $237.581   $237.58   $237.60   $237.60  
  Purchase #5 $176.67   6.388%   $187.9557   $187.96   $187.95   $188.00  
  Purchase #6 $224.26   7.494%   $241.066   $241.07   $241.05   $241.10  
  Purchase #7 $62.86   13.682%   $71.4605   $71.46   $71.45   $71.50  
  7 purchase totals = $952.07       $1,038.1456   $1,038.15   $1,038.15   $1,038.30