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 $249.99   4.862%   $262.1445   $262.14   $262.15   $262.10  
  Purchase #2 $233.69   6.570%   $249.0434   $249.04   $249.05   $249.00  
  Purchase #3 $153.95   8.869%   $167.6038   $167.60   $167.60   $167.60  
  Purchase #4 $39.51   10.386%   $43.6135   $43.61   $43.60   $43.60  
  Purchase #5 $125.54   12.216%   $140.876   $140.88   $140.90   $140.90  
  Purchase #6 $24.72   7.806%   $26.6496   $26.65   $26.65   $26.60  
  Purchase #7 $196.59   10.568%   $217.3656   $217.37   $217.35   $217.40  
  7 purchase totals = $1,023.99       $1,107.2964   $1,107.29   $1,107.30   $1,107.20