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 $241.39   11.574%   $269.3285   $269.33   $269.35   $269.30  
  Purchase #2 $59.36   8.514%   $64.4139   $64.41   $64.40   $64.40  
  Purchase #3 $127.63   4.359%   $133.1934   $133.19   $133.20   $133.20  
  Purchase #4 $242.62   12.385%   $272.6685   $272.67   $272.65   $272.70  
  Purchase #5 $80.51   9.215%   $87.929   $87.93   $87.95   $87.90  
  Purchase #6 $112.84   5.199%   $118.7066   $118.71   $118.70   $118.70  
  Purchase #7 $179.81   10.155%   $198.0697   $198.07   $198.05   $198.10  
  7 purchase totals = $1,044.16       $1,144.3096   $1,144.31   $1,144.30   $1,144.30