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 $241.99   11.167%   $269.013   $269.01   $269.00   $269.00  
  Purchase #2 $91.67   9.850%   $100.6995   $100.70   $100.70   $100.70  
  Purchase #3 $65.88   7.338%   $70.7143   $70.71   $70.70   $70.70  
  Purchase #4 $199.34   8.797%   $216.8759   $216.88   $216.90   $216.90  
  Purchase #5 $60.40   13.663%   $68.6525   $68.65   $68.65   $68.70  
  Purchase #6 $47.35   7.509%   $50.9055   $50.91   $50.90   $50.90  
  Purchase #7 $80.90   7.576%   $87.029   $87.03   $87.05   $87.00  
  7 purchase totals = $787.53       $863.8897   $863.89   $863.90   $863.90