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 $55.82   13.802%   $63.5243   $63.52   $63.50   $63.50  
  Purchase #2 $94.75   7.124%   $101.5   $101.50   $101.50   $101.50  
  Purchase #3 $56.30   12.661%   $63.4281   $63.43   $63.45   $63.40  
  Purchase #4 $5.86   7.859%   $6.3205   $6.32   $6.30   $6.30  
  Purchase #5 $30.94   12.593%   $34.8363   $34.84   $34.85   $34.80  
  Purchase #6 $162.50   10.156%   $179.0035   $179.00   $179.00   $179.00  
  Purchase #7 $43.99   8.213%   $47.6029   $47.60   $47.60   $47.60  
  7 purchase totals = $450.16       $496.2156   $496.21   $496.20   $496.10