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 $71.61   12.528%   $80.5813   $80.58   $80.60   $80.60  
  Purchase #2 $223.62   9.857%   $245.6622   $245.66   $245.65   $245.70  
  Purchase #3 $46.53   6.874%   $49.7285   $49.73   $49.75   $49.70  
  Purchase #4 $60.25   6.524%   $64.1807   $64.18   $64.20   $64.20  
  Purchase #5 $88.32   12.319%   $99.2001   $99.20   $99.20   $99.20  
  Purchase #6 $32.77   11.532%   $36.549   $36.55   $36.55   $36.50  
  Purchase #7 $177.71   4.223%   $185.2147   $185.21   $185.20   $185.20  
  7 purchase totals = $700.81       $761.1165   $761.11   $761.15   $761.10