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 $249.33   13.236%   $282.3313   $282.33   $282.35   $282.30  
  Purchase #2 $181.58   6.792%   $193.9129   $193.91   $193.90   $193.90  
  Purchase #3 $26.44   7.690%   $28.4732   $28.47   $28.45   $28.50  
  Purchase #4 $39.90   12.282%   $44.8005   $44.80   $44.80   $44.80  
  Purchase #5 $218.40   5.368%   $230.1237   $230.12   $230.10   $230.10  
  Purchase #6 $200.78   3.143%   $207.0905   $207.09   $207.10   $207.10  
  Purchase #7 $27.70   8.800%   $30.1376   $30.14   $30.15   $30.10  
  7 purchase totals = $944.13       $1,016.8697   $1,016.86   $1,016.85   $1,016.80