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 $44.28   13.394%   $50.2109   $50.21   $50.20   $50.20  
  Purchase #2 $87.72   7.499%   $94.2981   $94.30   $94.30   $94.30  
  Purchase #3 $107.33   4.483%   $112.1416   $112.14   $112.15   $112.10  
  Purchase #4 $228.91   7.440%   $245.9409   $245.94   $245.95   $245.90  
  Purchase #5 $185.73   8.222%   $201.0007   $201.00   $201.00   $201.00  
  Purchase #6 $109.27   12.613%   $123.0522   $123.05   $123.05   $123.10  
  Purchase #7 $118.84   13.619%   $135.0248   $135.02   $135.00   $135.00  
  7 purchase totals = $882.08       $961.6692   $961.66   $961.65   $961.60