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 $232.75   8.128%   $251.6679   $251.67   $251.65   $251.70  
  Purchase #2 $195.57   9.268%   $213.6954   $213.70   $213.70   $213.70  
  Purchase #3 $122.62   9.183%   $133.8802   $133.88   $133.90   $133.90  
  Purchase #4 $28.34   6.775%   $30.26   $30.26   $30.25   $30.30  
  Purchase #5 $176.99   9.452%   $193.7191   $193.72   $193.70   $193.70  
  Purchase #6 $106.30   11.289%   $118.3002   $118.30   $118.30   $118.30  
  Purchase #7 $231.81   5.169%   $243.7923   $243.79   $243.80   $243.80  
  7 purchase totals = $1,094.38       $1,185.3151   $1,185.32   $1,185.30   $1,185.40