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 $96.51   12.732%   $108.7977   $108.80   $108.80   $108.80  
  Purchase #2 $122.38   11.535%   $136.4965   $136.50   $136.50   $136.50  
  Purchase #3 $199.56   11.191%   $221.8928   $221.89   $221.90   $221.90  
  Purchase #4 $161.84   6.433%   $172.2512   $172.25   $172.25   $172.30  
  Purchase #5 $182.95   6.704%   $195.215   $195.22   $195.20   $195.20  
  Purchase #6 $61.97   6.495%   $65.995   $66.00   $66.00   $66.00  
  Purchase #7 $77.84   10.534%   $86.0397   $86.04   $86.05   $86.00  
  7 purchase totals = $903.05       $986.6879   $986.70   $986.70   $986.70