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 $222.88   10.479%   $246.2356   $246.24   $246.25   $246.20  
  Purchase #2 $100.47   4.437%   $104.9279   $104.93   $104.95   $104.90  
  Purchase #3 $87.37   9.435%   $95.6134   $95.61   $95.60   $95.60  
  Purchase #4 $135.44   8.683%   $147.2003   $147.20   $147.20   $147.20  
  Purchase #5 $86.84   12.342%   $97.5578   $97.56   $97.55   $97.60  
  Purchase #6 $224.58   11.712%   $250.8828   $250.88   $250.90   $250.90  
  Purchase #7 $210.26   5.160%   $221.1094   $221.11   $221.10   $221.10  
  7 purchase totals = $1,067.84       $1,163.5272   $1,163.53   $1,163.55   $1,163.50