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 $214.85   10.106%   $236.5627   $236.56   $236.55   $236.60  
  Purchase #2 $51.28   8.579%   $55.6793   $55.68   $55.70   $55.70  
  Purchase #3 $87.36   13.656%   $99.2899   $99.29   $99.30   $99.30  
  Purchase #4 $89.53   7.131%   $95.9144   $95.91   $95.90   $95.90  
  Purchase #5 $248.81   13.455%   $282.2874   $282.29   $282.30   $282.30  
  Purchase #6 $24.43   7.263%   $26.2044   $26.20   $26.20   $26.20  
  Purchase #7 $192.60   5.751%   $203.6764   $203.68   $203.70   $203.70  
  7 purchase totals = $908.86       $999.6145   $999.61   $999.65   $999.70