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 $66.49   11.273%   $73.9854   $73.99   $74.00   $74.00  
  Purchase #2 $117.73   9.268%   $128.6412   $128.64   $128.65   $128.60  
  Purchase #3 $216.74   9.548%   $237.4343   $237.43   $237.45   $237.40  
  Purchase #4 $240.88   4.296%   $251.2282   $251.23   $251.25   $251.20  
  Purchase #5 $236.90   10.277%   $261.2462   $261.25   $261.25   $261.20  
  Purchase #6 $98.26   6.699%   $104.8424   $104.84   $104.85   $104.80  
  Purchase #7 $78.77   12.495%   $88.6123   $88.61   $88.60   $88.60  
  7 purchase totals = $1,055.77       $1,145.9900   $1,145.99   $1,146.05   $1,145.80