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 $191.95   6.743%   $204.8932   $204.89   $204.90   $204.90  
  Purchase #2 $93.57   5.230%   $98.4637   $98.46   $98.45   $98.50  
  Purchase #3 $214.78   11.609%   $239.7138   $239.71   $239.70   $239.70  
  Purchase #4 $153.35   9.402%   $167.768   $167.77   $167.75   $167.80  
  Purchase #5 $152.47   3.545%   $157.8751   $157.88   $157.90   $157.90  
  Purchase #6 $29.32   11.602%   $32.7217   $32.72   $32.70   $32.70  
  Purchase #7 $135.65   4.450%   $141.6864   $141.69   $141.70   $141.70  
  7 purchase totals = $971.09       $1,043.1219   $1,043.12   $1,043.10   $1,043.20