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 $18.30   7.870%   $19.7402   $19.74   $19.75   $19.70  
  Purchase #2 $79.80   8.287%   $86.413   $86.41   $86.40   $86.40  
  Purchase #3 $128.39   12.279%   $144.155   $144.16   $144.15   $144.20  
  Purchase #4 $74.72   8.191%   $80.8403   $80.84   $80.85   $80.80  
  Purchase #5 $190.36   8.354%   $206.2627   $206.26   $206.25   $206.30  
  Purchase #6 $146.88   10.451%   $162.2304   $162.23   $162.25   $162.20  
  Purchase #7 $12.81   6.832%   $13.6852   $13.69   $13.70   $13.70  
  7 purchase totals = $651.26       $713.3268   $713.33   $713.35   $713.30