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 $189.60   8.672%   $206.0421   $206.04   $206.05   $206.00  
  Purchase #2 $225.94   6.524%   $240.6803   $240.68   $240.70   $240.70  
  Purchase #3 $98.42   7.713%   $106.0111   $106.01   $106.00   $106.00  
  Purchase #4 $210.67   7.309%   $226.0679   $226.07   $226.05   $226.10  
  Purchase #5 $176.80   5.761%   $186.9854   $186.99   $187.00   $187.00  
  Purchase #6 $145.76   5.176%   $153.3045   $153.30   $153.30   $153.30  
  Purchase #7 $27.61   11.226%   $30.7095   $30.71   $30.70   $30.70  
  7 purchase totals = $1,074.80       $1,149.8008   $1,149.80   $1,149.80   $1,149.80