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 $137.59   4.853%   $144.2672   $144.27   $144.25   $144.30  
  Purchase #2 $245.55   12.250%   $275.6299   $275.63   $275.65   $275.60  
  Purchase #3 $68.99   9.126%   $75.286   $75.29   $75.30   $75.30  
  Purchase #4 $191.37   8.563%   $207.757   $207.76   $207.75   $207.80  
  Purchase #5 $38.87   11.234%   $43.2367   $43.24   $43.25   $43.20  
  Purchase #6 $249.77   10.486%   $275.9609   $275.96   $275.95   $276.00  
  Purchase #7 $218.32   11.244%   $242.8679   $242.87   $242.85   $242.90  
  7 purchase totals = $1,150.46       $1,265.0056   $1,265.02   $1,265.00   $1,265.10