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 $54.41   10.727%   $60.2466   $60.25   $60.25   $60.20  
  Purchase #2 $6.72   6.758%   $7.1741   $7.17   $7.15   $7.20  
  Purchase #3 $139.38   8.418%   $151.113   $151.11   $151.10   $151.10  
  Purchase #4 $170.54   3.716%   $176.8773   $176.88   $176.90   $176.90  
  Purchase #5 $240.69   7.210%   $258.0437   $258.04   $258.05   $258.00  
  Purchase #6 $43.44   12.571%   $48.9008   $48.90   $48.90   $48.90  
  Purchase #7 $113.84   5.672%   $120.297   $120.30   $120.30   $120.30  
  7 purchase totals = $769.02       $822.6525   $822.65   $822.65   $822.60