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 $192.60   6.615%   $205.3405   $205.34   $205.35   $205.30  
  Purchase #2 $167.75   4.813%   $175.8238   $175.82   $175.80   $175.80  
  Purchase #3 $88.31   5.473%   $93.1432   $93.14   $93.15   $93.10  
  Purchase #4 $124.28   7.623%   $133.7539   $133.75   $133.75   $133.80  
  Purchase #5 $113.42   10.607%   $125.4505   $125.45   $125.45   $125.50  
  Purchase #6 $215.87   12.483%   $242.8171   $242.82   $242.80   $242.80  
  Purchase #7 $218.34   8.864%   $237.6937   $237.69   $237.70   $237.70  
  7 purchase totals = $1,120.57       $1,214.0227   $1,214.01   $1,214.00   $1,214.00