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 $194.34   6.264%   $206.5135   $206.51   $206.50   $206.50  
  Purchase #2 $50.61   12.705%   $57.04   $57.04   $57.05   $57.00  
  Purchase #3 $216.34   7.278%   $232.0852   $232.09   $232.10   $232.10  
  Purchase #4 $56.84   13.678%   $64.6146   $64.61   $64.60   $64.60  
  Purchase #5 $67.56   13.514%   $76.6901   $76.69   $76.70   $76.70  
  Purchase #6 $23.64   5.769%   $25.0038   $25.00   $25.00   $25.00  
  Purchase #7 $232.26   3.187%   $239.6621   $239.66   $239.65   $239.70  
  7 purchase totals = $841.59       $901.6093   $901.60   $901.60   $901.60