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 $244.40   8.413%   $264.9614   $264.96   $264.95   $265.00  
  Purchase #2 $151.38   7.677%   $163.0014   $163.00   $163.00   $163.00  
  Purchase #3 $8.35   5.235%   $8.7871   $8.79   $8.80   $8.80  
  Purchase #4 $80.39   11.779%   $89.8591   $89.86   $89.85   $89.90  
  Purchase #5 $42.57   13.402%   $48.2752   $48.28   $48.30   $48.30  
  Purchase #6 $32.62   6.808%   $34.8408   $34.84   $34.85   $34.80  
  Purchase #7 $122.76   5.813%   $129.896   $129.90   $129.90   $129.90  
  7 purchase totals = $682.47       $739.6210   $739.63   $739.65   $739.70