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 $168.91   11.455%   $188.2586   $188.26   $188.25   $188.30  
  Purchase #2 $123.54   8.197%   $133.6666   $133.67   $133.65   $133.70  
  Purchase #3 $199.46   7.594%   $214.607   $214.61   $214.60   $214.60  
  Purchase #4 $20.26   11.117%   $22.5123   $22.51   $22.50   $22.50  
  Purchase #5 $145.79   11.353%   $162.3415   $162.34   $162.35   $162.30  
  Purchase #6 $138.35   9.866%   $151.9996   $152.00   $152.00   $152.00  
  Purchase #7 $209.28   3.203%   $215.9832   $215.98   $216.00   $216.00  
  7 purchase totals = $1,005.59       $1,089.3688   $1,089.37   $1,089.35   $1,089.40