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 $202.95   10.176%   $223.6022   $223.60   $223.60   $223.60  
  Purchase #2 $116.57   5.514%   $122.9977   $123.00   $123.00   $123.00  
  Purchase #3 $61.72   7.746%   $66.5008   $66.50   $66.50   $66.50  
  Purchase #4 $188.38   5.658%   $199.0385   $199.04   $199.05   $199.00  
  Purchase #5 $221.90   7.763%   $239.1261   $239.13   $239.15   $239.10  
  Purchase #6 $48.95   6.411%   $52.0882   $52.09   $52.10   $52.10  
  Purchase #7 $150.57   9.408%   $164.7356   $164.74   $164.75   $164.70  
  7 purchase totals = $991.04       $1,068.0891   $1,068.10   $1,068.15   $1,068.00