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 $195.35   3.534%   $202.2537   $202.25   $202.25   $202.30  
  Purchase #2 $115.68   10.256%   $127.5441   $127.54   $127.55   $127.50  
  Purchase #3 $18.56   11.288%   $20.6551   $20.66   $20.65   $20.70  
  Purchase #4 $212.47   3.660%   $220.2464   $220.25   $220.25   $220.20  
  Purchase #5 $11.47   13.555%   $13.0248   $13.02   $13.00   $13.00  
  Purchase #6 $123.70   11.225%   $137.5853   $137.59   $137.60   $137.60  
  Purchase #7 $23.33   9.725%   $25.5988   $25.60   $25.60   $25.60  
  7 purchase totals = $700.56       $746.9082   $746.91   $746.90   $746.90