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 $33.42   13.520%   $37.9384   $37.94   $37.95   $37.90  
  Purchase #2 $14.66   4.820%   $15.3666   $15.37   $15.35   $15.40  
  Purchase #3 $38.44   4.832%   $40.2974   $40.30   $40.30   $40.30  
  Purchase #4 $240.53   7.107%   $257.6245   $257.62   $257.60   $257.60  
  Purchase #5 $52.89   12.838%   $59.68   $59.68   $59.70   $59.70  
  Purchase #6 $174.87   9.610%   $191.675   $191.68   $191.70   $191.70  
  Purchase #7 $242.49   4.324%   $252.9753   $252.98   $253.00   $253.00  
  7 purchase totals = $797.30       $855.5572   $855.57   $855.60   $855.60