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 $89.81   8.348%   $97.3073   $97.31   $97.30   $97.30  
  Purchase #2 $144.66   6.113%   $153.5031   $153.50   $153.50   $153.50  
  Purchase #3 $58.79   7.783%   $63.3656   $63.37   $63.35   $63.40  
  Purchase #4 $166.59   8.772%   $181.2033   $181.20   $181.20   $181.20  
  Purchase #5 $187.70   11.302%   $208.9139   $208.91   $208.90   $208.90  
  Purchase #6 $180.63   6.250%   $191.9194   $191.92   $191.90   $191.90  
  Purchase #7 $107.28   12.629%   $120.8284   $120.83   $120.85   $120.80  
  7 purchase totals = $935.46       $1,017.0410   $1,017.04   $1,017.00   $1,017.00