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 $206.62   6.306%   $219.6495   $219.65   $219.65   $219.60  
  Purchase #2 $115.97   5.364%   $122.1906   $122.19   $122.20   $122.20  
  Purchase #3 $100.48   8.624%   $109.1454   $109.15   $109.15   $109.10  
  Purchase #4 $24.31   6.586%   $25.9111   $25.91   $25.90   $25.90  
  Purchase #5 $210.96   3.113%   $217.5272   $217.53   $217.55   $217.50  
  Purchase #6 $205.35   6.616%   $218.936   $218.94   $218.95   $218.90  
  Purchase #7 $242.37   9.874%   $266.3016   $266.30   $266.30   $266.30  
  7 purchase totals = $1,106.06       $1,179.6614   $1,179.67   $1,179.70   $1,179.50