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 $206.28   5.675%   $217.9864   $217.99   $218.00   $218.00  
  Purchase #2 $33.95   11.358%   $37.806   $37.81   $37.80   $37.80  
  Purchase #3 $141.61   10.745%   $156.826   $156.83   $156.85   $156.80  
  Purchase #4 $115.98   11.335%   $129.1263   $129.13   $129.15   $129.10  
  Purchase #5 $244.70   7.625%   $263.3584   $263.36   $263.35   $263.40  
  Purchase #6 $67.25   9.613%   $73.7147   $73.71   $73.70   $73.70  
  Purchase #7 $115.61   8.208%   $125.0993   $125.10   $125.10   $125.10  
  7 purchase totals = $925.38       $1,003.9171   $1,003.93   $1,003.95   $1,003.90