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 $88.93   10.510%   $98.2765   $98.28   $98.30   $98.30  
  Purchase #2 $19.97   3.683%   $20.7055   $20.71   $20.70   $20.70  
  Purchase #3 $81.37   5.493%   $85.8397   $85.84   $85.85   $85.80  
  Purchase #4 $50.36   12.224%   $56.516   $56.52   $56.50   $56.50  
  Purchase #5 $231.94   3.685%   $240.487   $240.49   $240.50   $240.50  
  Purchase #6 $176.52   6.294%   $187.6302   $187.63   $187.65   $187.60  
  Purchase #7 $249.91   3.118%   $257.7022   $257.70   $257.70   $257.70  
  7 purchase totals = $899.00       $947.1571   $947.17   $947.20   $947.10