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 $122.46   6.396%   $130.2925   $130.29   $130.30   $130.30  
  Purchase #2 $211.40   9.440%   $231.3562   $231.36   $231.35   $231.40  
  Purchase #3 $207.35   4.651%   $216.9938   $216.99   $217.00   $217.00  
  Purchase #4 $47.49   11.340%   $52.8754   $52.88   $52.90   $52.90  
  Purchase #5 $149.99   4.555%   $156.822   $156.82   $156.80   $156.80  
  Purchase #6 $26.95   10.581%   $29.8016   $29.80   $29.80   $29.80  
  Purchase #7 $136.55   10.698%   $151.1581   $151.16   $151.15   $151.20  
  7 purchase totals = $902.19       $969.2996   $969.30   $969.30   $969.40