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 $202.92   6.557%   $216.2255   $216.23   $216.25   $216.20  
  Purchase #2 $63.25   3.285%   $65.3278   $65.33   $65.35   $65.30  
  Purchase #3 $77.76   9.147%   $84.8727   $84.87   $84.85   $84.90  
  Purchase #4 $148.26   9.203%   $161.9044   $161.90   $161.90   $161.90  
  Purchase #5 $83.61   12.736%   $94.2586   $94.26   $94.25   $94.30  
  Purchase #6 $150.26   9.478%   $164.5016   $164.50   $164.50   $164.50  
  Purchase #7 $15.66   12.363%   $17.596   $17.60   $17.60   $17.60  
  7 purchase totals = $741.72       $804.6866   $804.69   $804.70   $804.70