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 $208.69   8.169%   $225.7379   $225.74   $225.75   $225.70  
  Purchase #2 $166.45   6.476%   $177.2293   $177.23   $177.25   $177.20  
  Purchase #3 $145.75   5.575%   $153.8756   $153.88   $153.90   $153.90  
  Purchase #4 $30.72   11.146%   $34.1441   $34.14   $34.15   $34.10  
  Purchase #5 $213.68   12.459%   $240.3024   $240.30   $240.30   $240.30  
  Purchase #6 $95.79   6.137%   $101.6686   $101.67   $101.65   $101.70  
  Purchase #7 $152.97   3.422%   $158.2046   $158.20   $158.20   $158.20  
  7 purchase totals = $1,014.05       $1,091.1625   $1,091.16   $1,091.20   $1,091.10