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 $188.51   6.615%   $200.9799   $200.98   $201.00   $201.00  
  Purchase #2 $183.78   11.669%   $205.2253   $205.23   $205.25   $205.20  
  Purchase #3 $112.82   5.639%   $119.1819   $119.18   $119.20   $119.20  
  Purchase #4 $233.87   7.164%   $250.6244   $250.62   $250.60   $250.60  
  Purchase #5 $171.45   11.447%   $191.0759   $191.08   $191.10   $191.10  
  Purchase #6 $196.33   11.190%   $218.2993   $218.30   $218.30   $218.30  
  Purchase #7 $95.42   3.254%   $98.525   $98.53   $98.55   $98.50  
  7 purchase totals = $1,182.18       $1,283.9117   $1,283.92   $1,284.00   $1,283.90