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 $87.41   6.759%   $93.318   $93.32   $93.30   $93.30  
  Purchase #2 $161.53   10.463%   $178.4309   $178.43   $178.45   $178.40  
  Purchase #3 $119.95   4.435%   $125.2698   $125.27   $125.25   $125.30  
  Purchase #4 $81.62   6.291%   $86.7547   $86.75   $86.75   $86.80  
  Purchase #5 $195.42   3.830%   $202.9046   $202.90   $202.90   $202.90  
  Purchase #6 $222.94   10.457%   $246.2528   $246.25   $246.25   $246.30  
  Purchase #7 $145.53   7.595%   $156.583   $156.58   $156.60   $156.60  
  7 purchase totals = $1,014.40       $1,089.5138   $1,089.50   $1,089.50   $1,089.60