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 $60.56   10.136%   $66.6984   $66.70   $66.70   $66.70  
  Purchase #2 $231.70   11.832%   $259.1147   $259.11   $259.10   $259.10  
  Purchase #3 $214.37   11.819%   $239.7064   $239.71   $239.70   $239.70  
  Purchase #4 $132.33   11.624%   $147.712   $147.71   $147.70   $147.70  
  Purchase #5 $24.61   3.862%   $25.5604   $25.56   $25.55   $25.60  
  Purchase #6 $141.28   7.265%   $151.544   $151.54   $151.55   $151.50  
  Purchase #7 $122.98   6.430%   $130.8876   $130.89   $130.90   $130.90  
  7 purchase totals = $927.83       $1,021.2235   $1,021.22   $1,021.20   $1,021.20