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 $63.95   8.425%   $69.3378   $69.34   $69.35   $69.30  
  Purchase #2 $201.62   11.678%   $225.1652   $225.17   $225.15   $225.20  
  Purchase #3 $50.25   5.348%   $52.9374   $52.94   $52.95   $52.90  
  Purchase #4 $233.87   8.378%   $253.4636   $253.46   $253.45   $253.50  
  Purchase #5 $202.68   5.639%   $214.1091   $214.11   $214.10   $214.10  
  Purchase #6 $32.74   6.668%   $34.9231   $34.92   $34.90   $34.90  
  Purchase #7 $135.51   4.560%   $141.6893   $141.69   $141.70   $141.70  
  7 purchase totals = $920.62       $991.6255   $991.63   $991.60   $991.60