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 $218.67   10.630%   $241.9146   $241.91   $241.90   $241.90  
  Purchase #2 $182.90   13.176%   $206.9989   $207.00   $207.00   $207.00  
  Purchase #3 $247.80   7.182%   $265.597   $265.60   $265.60   $265.60  
  Purchase #4 $133.68   6.687%   $142.6192   $142.62   $142.60   $142.60  
  Purchase #5 $68.93   11.747%   $77.0272   $77.03   $77.05   $77.00  
  Purchase #6 $161.28   4.736%   $168.9182   $168.92   $168.90   $168.90  
  Purchase #7 $35.79   9.817%   $39.3035   $39.30   $39.30   $39.30  
  7 purchase totals = $1,049.05       $1,142.3786   $1,142.38   $1,142.35   $1,142.30