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 $56.82   4.848%   $59.5746   $59.57   $59.55   $59.60  
  Purchase #2 $44.85   11.854%   $50.1665   $50.17   $50.15   $50.20  
  Purchase #3 $217.55   7.629%   $234.1469   $234.15   $234.15   $234.10  
  Purchase #4 $32.63   10.424%   $36.0314   $36.03   $36.05   $36.00  
  Purchase #5 $183.96   9.532%   $201.4951   $201.50   $201.50   $201.50  
  Purchase #6 $229.59   5.132%   $241.3726   $241.37   $241.35   $241.40  
  Purchase #7 $110.27   3.658%   $114.3037   $114.30   $114.30   $114.30  
  7 purchase totals = $875.67       $937.0908   $937.09   $937.05   $937.10