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 $208.58   5.756%   $220.5859   $220.59   $220.60   $220.60  
  Purchase #2 $210.72   11.415%   $234.7737   $234.77   $234.75   $234.80  
  Purchase #3 $28.34   4.328%   $29.5666   $29.57   $29.55   $29.60  
  Purchase #4 $224.74   5.412%   $236.9029   $236.90   $236.90   $236.90  
  Purchase #5 $11.44   9.840%   $12.5657   $12.57   $12.55   $12.60  
  Purchase #6 $174.93   5.614%   $184.7506   $184.75   $184.75   $184.80  
  Purchase #7 $86.91   5.253%   $91.4754   $91.48   $91.50   $91.50  
  7 purchase totals = $945.66       $1,010.6208   $1,010.63   $1,010.60   $1,010.80