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 $85.60   9.414%   $93.6584   $93.66   $93.65   $93.70  
  Purchase #2 $24.61   6.777%   $26.2778   $26.28   $26.30   $26.30  
  Purchase #3 $244.58   6.175%   $259.6828   $259.68   $259.70   $259.70  
  Purchase #4 $117.43   4.325%   $122.5088   $122.51   $122.50   $122.50  
  Purchase #5 $130.45   10.644%   $144.3351   $144.34   $144.35   $144.30  
  Purchase #6 $145.58   7.772%   $156.8945   $156.89   $156.90   $156.90  
  Purchase #7 $156.89   4.834%   $164.4741   $164.47   $164.45   $164.50  
  7 purchase totals = $905.14       $967.8315   $967.83   $967.85   $967.90