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 $214.87   3.139%   $221.6148   $221.61   $221.60   $221.60  
  Purchase #2 $75.55   3.574%   $78.2502   $78.25   $78.25   $78.30  
  Purchase #3 $24.26   4.607%   $25.3777   $25.38   $25.40   $25.40  
  Purchase #4 $129.48   5.294%   $136.3347   $136.33   $136.35   $136.30  
  Purchase #5 $56.84   4.610%   $59.4603   $59.46   $59.45   $59.50  
  Purchase #6 $206.47   8.762%   $224.5609   $224.56   $224.55   $224.60  
  Purchase #7 $201.34   6.529%   $214.4855   $214.49   $214.50   $214.50  
  7 purchase totals = $908.81       $960.0841   $960.08   $960.10   $960.20