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 $231.99   5.196%   $244.0442   $244.04   $244.05   $244.00  
  Purchase #2 $111.67   13.319%   $126.5433   $126.54   $126.55   $126.50  
  Purchase #3 $15.54   5.282%   $16.3608   $16.36   $16.35   $16.40  
  Purchase #4 $139.66   13.267%   $158.1887   $158.19   $158.20   $158.20  
  Purchase #5 $122.76   7.491%   $131.956   $131.96   $131.95   $132.00  
  Purchase #6 $196.66   5.402%   $207.2836   $207.28   $207.30   $207.30  
  Purchase #7 $191.76   4.413%   $200.2224   $200.22   $200.20   $200.20  
  7 purchase totals = $1,010.04       $1,084.5990   $1,084.59   $1,084.60   $1,084.60