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 $108.53   9.822%   $119.1898   $119.19   $119.20   $119.20  
  Purchase #2 $26.25   9.342%   $28.7023   $28.70   $28.70   $28.70  
  Purchase #3 $93.93   5.653%   $99.2399   $99.24   $99.25   $99.20  
  Purchase #4 $245.49   5.630%   $259.3111   $259.31   $259.30   $259.30  
  Purchase #5 $221.40   13.156%   $250.5274   $250.53   $250.55   $250.50  
  Purchase #6 $12.33   13.788%   $14.0301   $14.03   $14.05   $14.00  
  Purchase #7 $249.71   9.835%   $274.269   $274.27   $274.25   $274.30  
  7 purchase totals = $957.64       $1,045.2696   $1,045.27   $1,045.30   $1,045.20