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 $245.66   12.849%   $277.2249   $277.22   $277.20   $277.20  
  Purchase #2 $171.29   9.145%   $186.9545   $186.95   $186.95   $187.00  
  Purchase #3 $53.49   11.584%   $59.6863   $59.69   $59.70   $59.70  
  Purchase #4 $100.91   11.599%   $112.6146   $112.61   $112.60   $112.60  
  Purchase #5 $238.88   7.834%   $257.5939   $257.59   $257.60   $257.60  
  Purchase #6 $250.94   9.518%   $274.8245   $274.82   $274.80   $274.80  
  Purchase #7 $173.85   7.187%   $186.3446   $186.34   $186.35   $186.30  
  7 purchase totals = $1,235.02       $1,355.2433   $1,355.22   $1,355.20   $1,355.20