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 $52.67   12.309%   $59.1532   $59.15   $59.15   $59.20  
  Purchase #2 $160.75   10.234%   $177.2012   $177.20   $177.20   $177.20  
  Purchase #3 $241.43   10.145%   $265.9231   $265.92   $265.90   $265.90  
  Purchase #4 $213.90   6.454%   $227.7051   $227.71   $227.70   $227.70  
  Purchase #5 $161.85   6.109%   $171.7374   $171.74   $171.75   $171.70  
  Purchase #6 $178.85   9.576%   $195.9767   $195.98   $196.00   $196.00  
  Purchase #7 $104.89   9.193%   $114.5325   $114.53   $114.55   $114.50  
  7 purchase totals = $1,114.34       $1,212.2292   $1,212.23   $1,212.25   $1,212.20