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 $249.31   8.244%   $269.8631   $269.86   $269.85   $269.90  
  Purchase #2 $108.75   4.547%   $113.6949   $113.69   $113.70   $113.70  
  Purchase #3 $207.90   8.394%   $225.3511   $225.35   $225.35   $225.40  
  Purchase #4 $10.96   11.735%   $12.2462   $12.25   $12.25   $12.20  
  Purchase #5 $53.74   8.170%   $58.1306   $58.13   $58.15   $58.10  
  Purchase #6 $230.62   4.849%   $241.8028   $241.80   $241.80   $241.80  
  Purchase #7 $227.63   8.470%   $246.9103   $246.91   $246.90   $246.90  
  7 purchase totals = $1,088.91       $1,167.9990   $1,167.99   $1,168.00   $1,168.00