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 $217.42   10.729%   $240.747   $240.75   $240.75   $240.70  
  Purchase #2 $242.77   3.392%   $251.0048   $251.00   $251.00   $251.00  
  Purchase #3 $239.26   13.454%   $271.45   $271.45   $271.45   $271.50  
  Purchase #4 $242.59   11.260%   $269.9056   $269.91   $269.90   $269.90  
  Purchase #5 $69.47   12.245%   $77.9766   $77.98   $78.00   $78.00  
  Purchase #6 $244.71   5.522%   $258.2229   $258.22   $258.20   $258.20  
  Purchase #7 $87.56   9.814%   $96.1531   $96.15   $96.15   $96.20  
  7 purchase totals = $1,343.78       $1,465.4600   $1,465.46   $1,465.45   $1,465.50