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 $35.87   3.543%   $37.1409   $37.14   $37.15   $37.10  
  Purchase #2 $214.65   5.103%   $225.6036   $225.60   $225.60   $225.60  
  Purchase #3 $145.57   9.822%   $159.8679   $159.87   $159.85   $159.90  
  Purchase #4 $209.81   12.402%   $235.8306   $235.83   $235.85   $235.80  
  Purchase #5 $59.62   8.784%   $64.857   $64.86   $64.85   $64.90  
  Purchase #6 $140.25   7.854%   $151.2652   $151.27   $151.25   $151.30  
  Purchase #7 $143.63   7.858%   $154.9164   $154.92   $154.90   $154.90  
  7 purchase totals = $949.40       $1,029.4816   $1,029.49   $1,029.45   $1,029.50