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 $184.81   10.105%   $203.4851   $203.49   $203.50   $203.50  
  Purchase #2 $103.39   13.719%   $117.5741   $117.57   $117.55   $117.60  
  Purchase #3 $61.97   4.221%   $64.5858   $64.59   $64.60   $64.60  
  Purchase #4 $230.32   4.164%   $239.9105   $239.91   $239.90   $239.90  
  Purchase #5 $97.66   4.448%   $102.0039   $102.00   $102.00   $102.00  
  Purchase #6 $77.37   6.391%   $82.3147   $82.31   $82.30   $82.30  
  Purchase #7 $204.28   5.123%   $214.7453   $214.75   $214.75   $214.70  
  7 purchase totals = $959.80       $1,024.6194   $1,024.62   $1,024.60   $1,024.60