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 $9.25   6.518%   $9.8529   $9.85   $9.85   $9.90  
  Purchase #2 $12.89   6.365%   $13.7104   $13.71   $13.70   $13.70  
  Purchase #3 $201.51   4.636%   $210.852   $210.85   $210.85   $210.90  
  Purchase #4 $239.35   9.823%   $262.8614   $262.86   $262.85   $262.90  
  Purchase #5 $247.77   3.164%   $255.6094   $255.61   $255.60   $255.60  
  Purchase #6 $198.40   11.295%   $220.8093   $220.81   $220.80   $220.80  
  Purchase #7 $139.53   4.177%   $145.3582   $145.36   $145.35   $145.40  
  7 purchase totals = $1,048.70       $1,119.0536   $1,119.05   $1,119.00   $1,119.20