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 $57.29   13.261%   $64.8872   $64.89   $64.90   $64.90  
  Purchase #2 $120.99   6.313%   $128.6281   $128.63   $128.65   $128.60  
  Purchase #3 $163.84   5.783%   $173.3149   $173.31   $173.30   $173.30  
  Purchase #4 $250.35   7.633%   $269.4592   $269.46   $269.45   $269.50  
  Purchase #5 $130.87   6.866%   $139.8555   $139.86   $139.85   $139.90  
  Purchase #6 $171.42   12.785%   $193.336   $193.34   $193.35   $193.30  
  Purchase #7 $74.36   3.229%   $76.7611   $76.76   $76.75   $76.80  
  7 purchase totals = $969.12       $1,046.2420   $1,046.25   $1,046.25   $1,046.30