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 $213.68   13.871%   $243.3196   $243.32   $243.30   $243.30  
  Purchase #2 $124.58   7.184%   $133.5298   $133.53   $133.55   $133.50  
  Purchase #3 $55.79   9.339%   $61.0002   $61.00   $61.00   $61.00  
  Purchase #4 $95.85   4.357%   $100.0262   $100.03   $100.05   $100.00  
  Purchase #5 $164.48   7.648%   $177.0594   $177.06   $177.05   $177.10  
  Purchase #6 $239.41   9.297%   $261.6679   $261.67   $261.65   $261.70  
  Purchase #7 $241.34   4.314%   $251.7514   $251.75   $251.75   $251.80  
  7 purchase totals = $1,135.13       $1,228.3545   $1,228.36   $1,228.35   $1,228.40