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 $164.27   11.377%   $182.959   $182.96   $182.95   $183.00  
  Purchase #2 $64.58   10.583%   $71.4145   $71.41   $71.40   $71.40  
  Purchase #3 $76.51   12.128%   $85.7891   $85.79   $85.80   $85.80  
  Purchase #4 $88.56   12.665%   $99.7761   $99.78   $99.80   $99.80  
  Purchase #5 $240.83   11.374%   $268.222   $268.22   $268.20   $268.20  
  Purchase #6 $147.78   6.273%   $157.0502   $157.05   $157.05   $157.10  
  Purchase #7 $120.70   4.316%   $125.9094   $125.91   $125.90   $125.90  
  7 purchase totals = $903.23       $991.1203   $991.12   $991.10   $991.20