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 $174.67   4.554%   $182.6245   $182.62   $182.60   $182.60  
  Purchase #2 $96.85   6.639%   $103.2799   $103.28   $103.30   $103.30  
  Purchase #3 $113.70   10.673%   $125.8352   $125.84   $125.85   $125.80  
  Purchase #4 $33.45   13.606%   $38.0012   $38.00   $38.00   $38.00  
  Purchase #5 $223.98   6.699%   $238.9844   $238.98   $239.00   $239.00  
  Purchase #6 $78.91   8.440%   $85.57   $85.57   $85.55   $85.60  
  Purchase #7 $239.62   8.867%   $260.8671   $260.87   $260.85   $260.90  
  7 purchase totals = $961.18       $1,035.1623   $1,035.16   $1,035.15   $1,035.20