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 $68.86   4.494%   $71.9546   $71.95   $71.95   $72.00  
  Purchase #2 $56.38   7.830%   $60.7946   $60.79   $60.80   $60.80  
  Purchase #3 $202.65   9.180%   $221.2533   $221.25   $221.25   $221.30  
  Purchase #4 $40.89   8.338%   $44.2994   $44.30   $44.30   $44.30  
  Purchase #5 $29.41   5.779%   $31.1096   $31.11   $31.10   $31.10  
  Purchase #6 $78.57   12.395%   $88.3088   $88.31   $88.30   $88.30  
  Purchase #7 $239.26   6.652%   $255.1756   $255.18   $255.20   $255.20  
  7 purchase totals = $716.02       $772.8959   $772.89   $772.90   $773.00