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 $191.99   10.559%   $212.2622   $212.26   $212.25   $212.30  
  Purchase #2 $25.56   11.470%   $28.4917   $28.49   $28.50   $28.50  
  Purchase #3 $82.95   7.489%   $89.1621   $89.16   $89.15   $89.20  
  Purchase #4 $191.32   5.557%   $201.9517   $201.95   $201.95   $202.00  
  Purchase #5 $205.64   4.719%   $215.3442   $215.34   $215.35   $215.30  
  Purchase #6 $119.57   5.116%   $125.6872   $125.69   $125.70   $125.70  
  Purchase #7 $157.41   3.416%   $162.7871   $162.79   $162.80   $162.80  
  7 purchase totals = $974.44       $1,035.6862   $1,035.68   $1,035.70   $1,035.80