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 $150.58   9.614%   $165.0568   $165.06   $165.05   $165.10  
  Purchase #2 $41.83   11.401%   $46.599   $46.60   $46.60   $46.60  
  Purchase #3 $113.28   11.856%   $126.7105   $126.71   $126.70   $126.70  
  Purchase #4 $238.43   3.525%   $246.8347   $246.83   $246.85   $246.80  
  Purchase #5 $43.75   9.448%   $47.8835   $47.88   $47.90   $47.90  
  Purchase #6 $131.72   13.554%   $149.5733   $149.57   $149.55   $149.60  
  Purchase #7 $237.28   6.745%   $253.2845   $253.28   $253.30   $253.30  
  7 purchase totals = $956.87       $1,035.9423   $1,035.93   $1,035.95   $1,036.00