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 $217.45   6.465%   $231.5081   $231.51   $231.50   $231.50  
  Purchase #2 $197.73   7.316%   $212.1959   $212.20   $212.20   $212.20  
  Purchase #3 $9.55   12.629%   $10.7561   $10.76   $10.75   $10.80  
  Purchase #4 $43.47   6.267%   $46.1943   $46.19   $46.20   $46.20  
  Purchase #5 $88.69   5.155%   $93.262   $93.26   $93.25   $93.30  
  Purchase #6 $131.49   6.816%   $140.4524   $140.45   $140.45   $140.50  
  Purchase #7 $117.28   12.130%   $131.5061   $131.51   $131.50   $131.50  
  7 purchase totals = $805.66       $865.8749   $865.88   $865.85   $866.00