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 $97.61   5.760%   $103.2323   $103.23   $103.25   $103.20  
  Purchase #2 $226.55   8.524%   $245.8611   $245.86   $245.85   $245.90  
  Purchase #3 $104.75   8.768%   $113.9345   $113.93   $113.95   $113.90  
  Purchase #4 $188.87   13.545%   $214.4524   $214.45   $214.45   $214.50  
  Purchase #5 $193.98   3.659%   $201.0777   $201.08   $201.10   $201.10  
  Purchase #6 $238.78   10.401%   $263.6155   $263.62   $263.60   $263.60  
  Purchase #7 $134.41   13.338%   $152.3376   $152.34   $152.35   $152.30  
  7 purchase totals = $1,184.95       $1,294.5111   $1,294.51   $1,294.55   $1,294.50