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 $87.36   7.491%   $93.9041   $93.90   $93.90   $93.90  
  Purchase #2 $81.45   12.400%   $91.5498   $91.55   $91.55   $91.50  
  Purchase #3 $202.71   12.615%   $228.2819   $228.28   $228.30   $228.30  
  Purchase #4 $206.91   5.116%   $217.4955   $217.50   $217.50   $217.50  
  Purchase #5 $176.38   6.518%   $187.8764   $187.88   $187.90   $187.90  
  Purchase #6 $177.32   7.559%   $190.7236   $190.72   $190.70   $190.70  
  Purchase #7 $218.27   3.204%   $225.2634   $225.26   $225.25   $225.30  
  7 purchase totals = $1,150.40       $1,235.0947   $1,235.09   $1,235.10   $1,235.10