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 $190.42   11.161%   $211.6728   $211.67   $211.65   $211.70  
  Purchase #2 $199.37   9.598%   $218.5055   $218.51   $218.50   $218.50  
  Purchase #3 $111.66   4.390%   $116.5619   $116.56   $116.55   $116.60  
  Purchase #4 $94.55   3.227%   $97.6011   $97.60   $97.60   $97.60  
  Purchase #5 $56.29   10.735%   $62.3327   $62.33   $62.35   $62.30  
  Purchase #6 $109.58   6.163%   $116.3334   $116.33   $116.35   $116.30  
  Purchase #7 $214.60   10.304%   $236.7124   $236.71   $236.70   $236.70  
  7 purchase totals = $976.47       $1,059.7198   $1,059.71   $1,059.70   $1,059.70