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 $57.84   9.104%   $63.1058   $63.11   $63.10   $63.10  
  Purchase #2 $95.61   11.657%   $106.7553   $106.76   $106.75   $106.80  
  Purchase #3 $229.49   10.393%   $253.3409   $253.34   $253.35   $253.30  
  Purchase #4 $136.74   3.639%   $141.716   $141.72   $141.70   $141.70  
  Purchase #5 $113.83   10.165%   $125.4008   $125.40   $125.40   $125.40  
  Purchase #6 $51.66   8.632%   $56.1193   $56.12   $56.10   $56.10  
  Purchase #7 $235.73   7.845%   $254.223   $254.22   $254.20   $254.20  
  7 purchase totals = $920.90       $1,000.6611   $1,000.67   $1,000.60   $1,000.60