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 $43.92   9.203%   $47.962   $47.96   $47.95   $48.00  
  Purchase #2 $8.99   10.192%   $9.9063   $9.91   $9.90   $9.90  
  Purchase #3 $56.43   8.689%   $61.3332   $61.33   $61.35   $61.30  
  Purchase #4 $238.65   3.812%   $247.7473   $247.75   $247.75   $247.70  
  Purchase #5 $208.66   11.308%   $232.2553   $232.26   $232.25   $232.30  
  Purchase #6 $95.96   6.353%   $102.0563   $102.06   $102.05   $102.10  
  Purchase #7 $122.78   3.109%   $126.5972   $126.60   $126.60   $126.60  
  7 purchase totals = $775.39       $827.8576   $827.87   $827.85   $827.90