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 $222.56   12.219%   $249.7546   $249.75   $249.75   $249.80  
  Purchase #2 $25.63   6.346%   $27.2565   $27.26   $27.25   $27.30  
  Purchase #3 $13.90   3.241%   $14.3505   $14.35   $14.35   $14.40  
  Purchase #4 $233.88   9.325%   $255.6893   $255.69   $255.70   $255.70  
  Purchase #5 $123.52   8.745%   $134.3218   $134.32   $134.30   $134.30  
  Purchase #6 $243.88   8.530%   $264.683   $264.68   $264.70   $264.70  
  Purchase #7 $221.92   11.486%   $247.4097   $247.41   $247.40   $247.40  
  7 purchase totals = $1,085.29       $1,193.4654   $1,193.46   $1,193.45   $1,193.60