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 $191.82   4.134%   $199.7498   $199.75   $199.75   $199.70  
  Purchase #2 $212.89   12.726%   $239.9824   $239.98   $240.00   $240.00  
  Purchase #3 $58.35   12.256%   $65.5014   $65.50   $65.50   $65.50  
  Purchase #4 $159.42   3.436%   $164.8977   $164.90   $164.90   $164.90  
  Purchase #5 $75.99   11.340%   $84.6073   $84.61   $84.60   $84.60  
  Purchase #6 $207.82   8.860%   $226.2329   $226.23   $226.25   $226.20  
  Purchase #7 $68.62   8.180%   $74.2331   $74.23   $74.25   $74.20  
  7 purchase totals = $974.91       $1,055.2046   $1,055.20   $1,055.25   $1,055.10