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 $48.87   3.463%   $50.5624   $50.56   $50.55   $50.60  
  Purchase #2 $194.56   11.495%   $216.9247   $216.92   $216.90   $216.90  
  Purchase #3 $185.81   10.275%   $204.902   $204.90   $204.90   $204.90  
  Purchase #4 $74.47   6.656%   $79.4267   $79.43   $79.45   $79.40  
  Purchase #5 $17.75   8.372%   $19.236   $19.24   $19.25   $19.20  
  Purchase #6 $238.47   13.829%   $271.448   $271.45   $271.45   $271.40  
  Purchase #7 $118.41   3.868%   $122.9901   $122.99   $123.00   $123.00  
  7 purchase totals = $878.34       $965.4899   $965.49   $965.50   $965.40