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 $227.87   12.451%   $256.2421   $256.24   $256.25   $256.20  
  Purchase #2 $188.92   4.423%   $197.2759   $197.28   $197.30   $197.30  
  Purchase #3 $168.42   7.846%   $181.6342   $181.63   $181.65   $181.60  
  Purchase #4 $142.85   6.804%   $152.5695   $152.57   $152.55   $152.60  
  Purchase #5 $142.40   3.849%   $147.881   $147.88   $147.90   $147.90  
  Purchase #6 $70.98   3.324%   $73.3394   $73.34   $73.35   $73.30  
  Purchase #7 $34.27   10.125%   $37.7398   $37.74   $37.75   $37.70  
  7 purchase totals = $975.71       $1,046.6819   $1,046.68   $1,046.75   $1,046.60