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 $68.57   7.473%   $73.6942   $73.69   $73.70   $73.70  
  Purchase #2 $59.25   8.254%   $64.1405   $64.14   $64.15   $64.10  
  Purchase #3 $63.67   8.170%   $68.8718   $68.87   $68.85   $68.90  
  Purchase #4 $104.99   5.327%   $110.5828   $110.58   $110.60   $110.60  
  Purchase #5 $63.98   3.242%   $66.0542   $66.05   $66.05   $66.10  
  Purchase #6 $157.29   10.702%   $174.1232   $174.12   $174.10   $174.10  
  Purchase #7 $27.71   10.394%   $30.5902   $30.59   $30.60   $30.60  
  7 purchase totals = $545.46       $588.0569   $588.04   $588.05   $588.10