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 $246.91   10.329%   $272.4133   $272.41   $272.40   $272.40  
  Purchase #2 $78.53   8.117%   $84.9043   $84.90   $84.90   $84.90  
  Purchase #3 $162.44   4.204%   $169.269   $169.27   $169.25   $169.30  
  Purchase #4 $215.84   8.586%   $234.372   $234.37   $234.35   $234.40  
  Purchase #5 $52.32   6.252%   $55.591   $55.59   $55.60   $55.60  
  Purchase #6 $63.86   8.687%   $69.4075   $69.41   $69.40   $69.40  
  Purchase #7 $146.43   10.736%   $162.1507   $162.15   $162.15   $162.20  
  7 purchase totals = $966.33       $1,048.1078   $1,048.10   $1,048.05   $1,048.20