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 $90.64   8.330%   $98.1903   $98.19   $98.20   $98.20  
  Purchase #2 $224.28   3.334%   $231.7575   $231.76   $231.75   $231.80  
  Purchase #3 $172.57   5.792%   $182.5653   $182.57   $182.55   $182.60  
  Purchase #4 $55.73   13.738%   $63.3862   $63.39   $63.40   $63.40  
  Purchase #5 $67.83   11.323%   $75.5104   $75.51   $75.50   $75.50  
  Purchase #6 $208.87   7.213%   $223.9358   $223.94   $223.95   $223.90  
  Purchase #7 $179.86   11.828%   $201.1338   $201.13   $201.15   $201.10  
  7 purchase totals = $999.78       $1,076.4793   $1,076.49   $1,076.50   $1,076.50