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 $51.73   4.103%   $53.8525   $53.85   $53.85   $53.90  
  Purchase #2 $88.75   5.856%   $93.9472   $93.95   $93.95   $93.90  
  Purchase #3 $157.73   8.200%   $170.6639   $170.66   $170.65   $170.70  
  Purchase #4 $121.42   5.168%   $127.695   $127.70   $127.70   $127.70  
  Purchase #5 $71.25   5.765%   $75.3576   $75.36   $75.35   $75.40  
  Purchase #6 $174.86   4.632%   $182.9595   $182.96   $182.95   $183.00  
  Purchase #7 $238.83   3.345%   $246.8189   $246.82   $246.80   $246.80  
  7 purchase totals = $904.57       $951.2946   $951.30   $951.25   $951.40