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 $88.64   5.587%   $93.5923   $93.59   $93.60   $93.60  
  Purchase #2 $156.86   6.272%   $166.6983   $166.70   $166.70   $166.70  
  Purchase #3 $240.43   11.134%   $267.1995   $267.20   $267.20   $267.20  
  Purchase #4 $195.77   11.594%   $218.4676   $218.47   $218.45   $218.50  
  Purchase #5 $144.88   7.688%   $156.0184   $156.02   $156.00   $156.00  
  Purchase #6 $77.35   10.406%   $85.399   $85.40   $85.40   $85.40  
  Purchase #7 $196.66   9.824%   $215.9799   $215.98   $216.00   $216.00  
  7 purchase totals = $1,100.59       $1,203.3550   $1,203.36   $1,203.35   $1,203.40