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 $91.82   6.722%   $97.9921   $97.99   $98.00   $98.00  
  Purchase #2 $144.72   13.594%   $164.3932   $164.39   $164.40   $164.40  
  Purchase #3 $214.49   12.212%   $240.6835   $240.68   $240.70   $240.70  
  Purchase #4 $111.45   6.782%   $119.0085   $119.01   $119.00   $119.00  
  Purchase #5 $91.94   7.674%   $98.9955   $99.00   $99.00   $99.00  
  Purchase #6 $176.33   9.831%   $193.665   $193.67   $193.65   $193.70  
  Purchase #7 $111.53   9.153%   $121.7383   $121.74   $121.75   $121.70  
  7 purchase totals = $942.28       $1,036.4761   $1,036.48   $1,036.50   $1,036.50