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 $246.95   11.369%   $275.0257   $275.03   $275.05   $275.00  
  Purchase #2 $29.87   4.689%   $31.2706   $31.27   $31.25   $31.30  
  Purchase #3 $194.43   8.439%   $210.8379   $210.84   $210.85   $210.80  
  Purchase #4 $166.37   6.369%   $176.9661   $176.97   $176.95   $177.00  
  Purchase #5 $140.37   9.685%   $153.9648   $153.96   $153.95   $154.00  
  Purchase #6 $25.68   8.763%   $27.9303   $27.93   $27.95   $27.90  
  Purchase #7 $20.25   9.497%   $22.1731   $22.17   $22.15   $22.20  
  7 purchase totals = $823.92       $898.1685   $898.17   $898.15   $898.20