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 $49.59   11.714%   $55.399   $55.40   $55.40   $55.40  
  Purchase #2 $194.96   9.873%   $214.2084   $214.21   $214.20   $214.20  
  Purchase #3 $197.83   12.702%   $222.9584   $222.96   $222.95   $223.00  
  Purchase #4 $50.64   13.104%   $57.2759   $57.28   $57.30   $57.30  
  Purchase #5 $226.31   9.229%   $247.1961   $247.20   $247.20   $247.20  
  Purchase #6 $48.71   5.211%   $51.2483   $51.25   $51.25   $51.20  
  Purchase #7 $111.96   6.248%   $118.9553   $118.96   $118.95   $119.00  
  7 purchase totals = $880.00       $967.2414   $967.26   $967.25   $967.30