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 $201.90   6.635%   $215.2961   $215.30   $215.30   $215.30  
  Purchase #2 $46.51   9.866%   $51.0987   $51.10   $51.10   $51.10  
  Purchase #3 $27.46   6.504%   $29.246   $29.25   $29.25   $29.20  
  Purchase #4 $59.99   7.685%   $64.6002   $64.60   $64.60   $64.60  
  Purchase #5 $85.78   12.272%   $96.3069   $96.31   $96.30   $96.30  
  Purchase #6 $217.57   6.186%   $231.0289   $231.03   $231.05   $231.00  
  Purchase #7 $234.33   6.679%   $249.9809   $249.98   $250.00   $250.00  
  7 purchase totals = $873.54       $937.5577   $937.57   $937.60   $937.50