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 $167.54   10.130%   $184.5118   $184.51   $184.50   $184.50  
  Purchase #2 $31.41   12.454%   $35.3218   $35.32   $35.30   $35.30  
  Purchase #3 $179.59   12.161%   $201.4299   $201.43   $201.45   $201.40  
  Purchase #4 $54.97   4.326%   $57.348   $57.35   $57.35   $57.30  
  Purchase #5 $44.38   9.612%   $48.6458   $48.65   $48.65   $48.60  
  Purchase #6 $91.80   13.316%   $104.0241   $104.02   $104.00   $104.00  
  Purchase #7 $205.26   6.657%   $218.9242   $218.92   $218.90   $218.90  
  7 purchase totals = $774.95       $850.2056   $850.20   $850.15   $850.00