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 $28.77   4.449%   $30.05   $30.05   $30.05   $30.10  
  Purchase #2 $187.53   5.620%   $198.0692   $198.07   $198.05   $198.10  
  Purchase #3 $203.70   12.799%   $229.7716   $229.77   $229.75   $229.80  
  Purchase #4 $170.53   3.635%   $176.7288   $176.73   $176.75   $176.70  
  Purchase #5 $85.82   3.378%   $88.719   $88.72   $88.70   $88.70  
  Purchase #6 $110.29   13.572%   $125.2586   $125.26   $125.25   $125.30  
  Purchase #7 $167.25   7.703%   $180.1333   $180.13   $180.15   $180.10  
  7 purchase totals = $953.89       $1,028.7305   $1,028.73   $1,028.70   $1,028.80