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 $205.62   9.647%   $225.4562   $225.46   $225.45   $225.50  
  Purchase #2 $216.41   11.668%   $241.6607   $241.66   $241.65   $241.70  
  Purchase #3 $87.77   5.402%   $92.5113   $92.51   $92.50   $92.50  
  Purchase #4 $44.74   9.315%   $48.9075   $48.91   $48.90   $48.90  
  Purchase #5 $75.58   6.198%   $80.2644   $80.26   $80.25   $80.30  
  Purchase #6 $79.51   3.196%   $82.0511   $82.05   $82.05   $82.10  
  Purchase #7 $204.96   5.134%   $215.4826   $215.48   $215.50   $215.50  
  7 purchase totals = $914.59       $986.3338   $986.33   $986.30   $986.50