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 $23.85   9.227%   $26.0506   $26.05   $26.05   $26.10  
  Purchase #2 $59.99   9.657%   $65.7832   $65.78   $65.80   $65.80  
  Purchase #3 $107.47   3.649%   $111.3916   $111.39   $111.40   $111.40  
  Purchase #4 $25.96   12.683%   $29.2525   $29.25   $29.25   $29.30  
  Purchase #5 $112.67   11.231%   $125.324   $125.32   $125.30   $125.30  
  Purchase #6 $100.90   9.527%   $110.5127   $110.51   $110.50   $110.50  
  Purchase #7 $118.90   7.322%   $127.6059   $127.61   $127.60   $127.60  
  7 purchase totals = $549.74       $595.9205   $595.91   $595.90   $596.00