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 $202.64   10.706%   $224.3346   $224.33   $224.35   $224.30  
  Purchase #2 $168.96   8.258%   $182.9127   $182.91   $182.90   $182.90  
  Purchase #3 $92.26   7.135%   $98.8428   $98.84   $98.85   $98.80  
  Purchase #4 $208.57   5.666%   $220.3876   $220.39   $220.40   $220.40  
  Purchase #5 $171.70   8.332%   $186.006   $186.01   $186.00   $186.00  
  Purchase #6 $101.69   4.226%   $105.9874   $105.99   $106.00   $106.00  
  Purchase #7 $200.92   9.167%   $219.3383   $219.34   $219.35   $219.30  
  7 purchase totals = $1,146.74       $1,237.8094   $1,237.81   $1,237.85   $1,237.70