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 $30.99   3.326%   $32.0207   $32.02   $32.00   $32.00  
  Purchase #2 $245.37   7.439%   $263.6231   $263.62   $263.60   $263.60  
  Purchase #3 $52.71   9.720%   $57.8334   $57.83   $57.85   $57.80  
  Purchase #4 $148.84   3.630%   $154.2429   $154.24   $154.25   $154.20  
  Purchase #5 $73.94   11.645%   $82.5503   $82.55   $82.55   $82.60  
  Purchase #6 $147.48   8.728%   $160.3521   $160.35   $160.35   $160.40  
  Purchase #7 $232.55   7.800%   $250.6889   $250.69   $250.70   $250.70  
  7 purchase totals = $931.88       $1,001.3114   $1,001.30   $1,001.30   $1,001.30