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 $116.67   5.191%   $122.7263   $122.73   $122.75   $122.70  
  Purchase #2 $52.50   8.428%   $56.9247   $56.92   $56.90   $56.90  
  Purchase #3 $239.49   8.138%   $258.9797   $258.98   $259.00   $259.00  
  Purchase #4 $169.96   9.727%   $186.492   $186.49   $186.50   $186.50  
  Purchase #5 $101.76   8.232%   $110.1369   $110.14   $110.15   $110.10  
  Purchase #6 $13.99   9.245%   $15.2834   $15.28   $15.30   $15.30  
  Purchase #7 $235.39   4.746%   $246.5616   $246.56   $246.55   $246.60  
  7 purchase totals = $929.76       $997.1046   $997.10   $997.15   $997.10