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 $85.57   12.110%   $95.9325   $95.93   $95.95   $95.90  
  Purchase #2 $106.26   3.469%   $109.9462   $109.95   $109.95   $109.90  
  Purchase #3 $91.66   4.683%   $95.9524   $95.95   $95.95   $96.00  
  Purchase #4 $86.73   11.190%   $96.4351   $96.44   $96.45   $96.40  
  Purchase #5 $75.57   6.441%   $80.4375   $80.44   $80.45   $80.40  
  Purchase #6 $147.89   7.782%   $159.3988   $159.40   $159.40   $159.40  
  Purchase #7 $21.45   9.586%   $23.5062   $23.51   $23.50   $23.50  
  7 purchase totals = $615.13       $661.6087   $661.62   $661.65   $661.50