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 $168.50   8.262%   $182.4215   $182.42   $182.40   $182.40  
  Purchase #2 $30.95   4.770%   $32.4263   $32.43   $32.45   $32.40  
  Purchase #3 $117.69   11.455%   $131.1714   $131.17   $131.15   $131.20  
  Purchase #4 $218.36   7.784%   $235.3571   $235.36   $235.35   $235.40  
  Purchase #5 $160.35   12.828%   $180.9197   $180.92   $180.90   $180.90  
  Purchase #6 $64.77   5.841%   $68.5532   $68.55   $68.55   $68.60  
  Purchase #7 $192.43   7.260%   $206.4004   $206.40   $206.40   $206.40  
  7 purchase totals = $953.05       $1,037.2496   $1,037.25   $1,037.20   $1,037.30