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 $96.45   10.867%   $106.9312   $106.93   $106.95   $106.90  
  Purchase #2 $40.94   12.610%   $46.1025   $46.10   $46.10   $46.10  
  Purchase #3 $249.52   6.195%   $264.9778   $264.98   $265.00   $265.00  
  Purchase #4 $67.98   12.261%   $76.315   $76.32   $76.30   $76.30  
  Purchase #5 $78.79   9.799%   $86.5106   $86.51   $86.50   $86.50  
  Purchase #6 $233.78   3.102%   $241.0319   $241.03   $241.05   $241.00  
  Purchase #7 $140.31   5.307%   $147.7563   $147.76   $147.75   $147.80  
  7 purchase totals = $907.77       $969.6253   $969.63   $969.65   $969.60