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 $43.89   8.675%   $47.6975   $47.70   $47.70   $47.70  
  Purchase #2 $236.74   9.720%   $259.7511   $259.75   $259.75   $259.80  
  Purchase #3 $116.42   4.240%   $121.3562   $121.36   $121.35   $121.40  
  Purchase #4 $47.26   10.346%   $52.1495   $52.15   $52.15   $52.10  
  Purchase #5 $194.35   3.659%   $201.4613   $201.46   $201.45   $201.50  
  Purchase #6 $179.89   3.304%   $185.8336   $185.83   $185.85   $185.80  
  Purchase #7 $147.71   4.756%   $154.7351   $154.74   $154.75   $154.70  
  7 purchase totals = $966.26       $1,022.9843   $1,022.99   $1,023.00   $1,023.00