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 $246.92   8.822%   $268.7033   $268.70   $268.70   $268.70  
  Purchase #2 $218.81   10.255%   $241.249   $241.25   $241.25   $241.20  
  Purchase #3 $136.38   7.329%   $146.3753   $146.38   $146.40   $146.40  
  Purchase #4 $247.79   12.772%   $279.4377   $279.44   $279.45   $279.40  
  Purchase #5 $180.65   7.209%   $193.6731   $193.67   $193.65   $193.70  
  Purchase #6 $239.65   6.334%   $254.8294   $254.83   $254.85   $254.80  
  Purchase #7 $87.68   12.631%   $98.7549   $98.75   $98.75   $98.80  
  7 purchase totals = $1,357.88       $1,483.0227   $1,483.02   $1,483.05   $1,483.00