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 $66.85   9.566%   $73.2449   $73.24   $73.25   $73.20  
  Purchase #2 $130.37   13.509%   $147.9817   $147.98   $148.00   $148.00  
  Purchase #3 $240.56   11.511%   $268.2509   $268.25   $268.25   $268.30  
  Purchase #4 $139.74   9.296%   $152.7302   $152.73   $152.75   $152.70  
  Purchase #5 $184.33   13.151%   $208.5712   $208.57   $208.55   $208.60  
  Purchase #6 $42.42   4.281%   $44.236   $44.24   $44.25   $44.20  
  Purchase #7 $241.79   12.719%   $272.5433   $272.54   $272.55   $272.50  
  7 purchase totals = $1,046.06       $1,167.5582   $1,167.55   $1,167.60   $1,167.50