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 $71.69   6.799%   $76.5642   $76.56   $76.55   $76.60  
  Purchase #2 $29.86   12.683%   $33.6471   $33.65   $33.65   $33.60  
  Purchase #3 $97.76   7.557%   $105.1477   $105.15   $105.15   $105.10  
  Purchase #4 $184.68   10.141%   $203.4084   $203.41   $203.40   $203.40  
  Purchase #5 $214.83   10.749%   $237.9221   $237.92   $237.90   $237.90  
  Purchase #6 $111.43   6.621%   $118.8078   $118.81   $118.80   $118.80  
  Purchase #7 $227.90   13.728%   $259.1861   $259.19   $259.20   $259.20  
  7 purchase totals = $938.15       $1,034.6834   $1,034.69   $1,034.65   $1,034.60