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 $233.38   6.402%   $248.321   $248.32   $248.30   $248.30  
  Purchase #2 $31.49   11.106%   $34.9873   $34.99   $35.00   $35.00  
  Purchase #3 $193.71   9.230%   $211.5894   $211.59   $211.60   $211.60  
  Purchase #4 $236.40   12.174%   $265.1793   $265.18   $265.20   $265.20  
  Purchase #5 $159.85   11.261%   $177.8507   $177.85   $177.85   $177.90  
  Purchase #6 $227.33   5.422%   $239.6558   $239.66   $239.65   $239.70  
  Purchase #7 $19.81   10.515%   $21.893   $21.89   $21.90   $21.90  
  7 purchase totals = $1,101.97       $1,199.4765   $1,199.48   $1,199.50   $1,199.60