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 $221.56   11.124%   $246.2063   $246.21   $246.20   $246.20  
  Purchase #2 $71.74   12.395%   $80.6322   $80.63   $80.65   $80.60  
  Purchase #3 $228.64   12.439%   $257.0805   $257.08   $257.10   $257.10  
  Purchase #4 $46.46   12.235%   $52.1444   $52.14   $52.15   $52.10  
  Purchase #5 $82.48   12.153%   $92.5038   $92.50   $92.50   $92.50  
  Purchase #6 $95.90   8.414%   $103.969   $103.97   $103.95   $104.00  
  Purchase #7 $48.60   3.269%   $50.1887   $50.19   $50.20   $50.20  
  7 purchase totals = $795.38       $882.7249   $882.72   $882.75   $882.70