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 $24.63   6.458%   $26.2206   $26.22   $26.20   $26.20  
  Purchase #2 $54.80   4.370%   $57.1948   $57.19   $57.20   $57.20  
  Purchase #3 $248.84   3.123%   $256.6113   $256.61   $256.60   $256.60  
  Purchase #4 $216.37   10.182%   $238.4008   $238.40   $238.40   $238.40  
  Purchase #5 $221.60   3.597%   $229.571   $229.57   $229.55   $229.60  
  Purchase #6 $71.27   11.556%   $79.506   $79.51   $79.50   $79.50  
  Purchase #7 $125.52   11.684%   $140.1858   $140.19   $140.20   $140.20  
  7 purchase totals = $963.03       $1,027.6903   $1,027.69   $1,027.65   $1,027.70