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 $67.65   12.474%   $76.0887   $76.09   $76.10   $76.10  
  Purchase #2 $119.26   3.589%   $123.5402   $123.54   $123.55   $123.50  
  Purchase #3 $93.32   9.412%   $102.1033   $102.10   $102.10   $102.10  
  Purchase #4 $109.44   13.727%   $124.4628   $124.46   $124.45   $124.50  
  Purchase #5 $234.85   13.302%   $266.0897   $266.09   $266.10   $266.10  
  Purchase #6 $225.83   10.493%   $249.5263   $249.53   $249.55   $249.50  
  Purchase #7 $60.62   10.530%   $67.0033   $67.00   $67.00   $67.00  
  7 purchase totals = $910.97       $1,008.8143   $1,008.81   $1,008.85   $1,008.80