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 $58.35   4.508%   $60.9804   $60.98   $61.00   $61.00  
  Purchase #2 $81.42   5.142%   $85.6066   $85.61   $85.60   $85.60  
  Purchase #3 $57.97   8.750%   $63.0424   $63.04   $63.05   $63.00  
  Purchase #4 $197.74   7.332%   $212.2383   $212.24   $212.25   $212.20  
  Purchase #5 $113.40   9.196%   $123.8283   $123.83   $123.85   $123.80  
  Purchase #6 $157.71   13.416%   $178.8684   $178.87   $178.85   $178.90  
  Purchase #7 $95.40   9.215%   $104.1911   $104.19   $104.20   $104.20  
  7 purchase totals = $761.99       $828.7555   $828.76   $828.80   $828.70