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 $229.75   6.776%   $245.3179   $245.32   $245.30   $245.30  
  Purchase #2 $246.42   13.362%   $279.3466   $279.35   $279.35   $279.30  
  Purchase #3 $59.56   5.798%   $63.0133   $63.01   $63.00   $63.00  
  Purchase #4 $127.50   8.423%   $138.2393   $138.24   $138.25   $138.20  
  Purchase #5 $118.86   6.469%   $126.5491   $126.55   $126.55   $126.50  
  Purchase #6 $119.91   4.569%   $125.3887   $125.39   $125.40   $125.40  
  Purchase #7 $156.91   7.243%   $168.275   $168.28   $168.30   $168.30  
  7 purchase totals = $1,058.91       $1,146.1299   $1,146.14   $1,146.15   $1,146.00