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 $48.95   3.293%   $50.5619   $50.56   $50.55   $50.60  
  Purchase #2 $111.71   4.464%   $116.6967   $116.70   $116.70   $116.70  
  Purchase #3 $205.44   3.180%   $211.973   $211.97   $211.95   $212.00  
  Purchase #4 $13.54   13.701%   $15.3951   $15.40   $15.40   $15.40  
  Purchase #5 $99.25   4.332%   $103.5495   $103.55   $103.55   $103.50  
  Purchase #6 $182.66   10.366%   $201.5945   $201.59   $201.60   $201.60  
  Purchase #7 $115.43   10.774%   $127.8664   $127.87   $127.85   $127.90  
  7 purchase totals = $776.98       $827.6371   $827.64   $827.60   $827.70