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 $232.41   6.251%   $246.9379   $246.94   $246.95   $246.90  
  Purchase #2 $116.26   10.161%   $128.0732   $128.07   $128.05   $128.10  
  Purchase #3 $175.87   12.663%   $198.1404   $198.14   $198.15   $198.10  
  Purchase #4 $246.83   3.852%   $256.3379   $256.34   $256.35   $256.30  
  Purchase #5 $49.56   8.788%   $53.9153   $53.92   $53.90   $53.90  
  Purchase #6 $116.41   3.549%   $120.5414   $120.54   $120.55   $120.50  
  Purchase #7 $157.36   6.145%   $167.0298   $167.03   $167.05   $167.00  
  7 purchase totals = $1,094.70       $1,170.9759   $1,170.98   $1,171.00   $1,170.80