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 $212.65   12.847%   $239.9691   $239.97   $239.95   $240.00  
  Purchase #2 $66.40   10.528%   $73.3906   $73.39   $73.40   $73.40  
  Purchase #3 $7.95   6.727%   $8.4848   $8.48   $8.50   $8.50  
  Purchase #4 $246.86   6.865%   $263.8069   $263.81   $263.80   $263.80  
  Purchase #5 $182.76   12.585%   $205.7603   $205.76   $205.75   $205.80  
  Purchase #6 $51.68   7.239%   $55.4211   $55.42   $55.40   $55.40  
  Purchase #7 $184.57   9.443%   $201.9989   $202.00   $202.00   $202.00  
  7 purchase totals = $952.87       $1,048.8317   $1,048.83   $1,048.80   $1,048.90