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 $73.27   13.283%   $83.0025   $83.00   $83.00   $83.00  
  Purchase #2 $231.70   6.469%   $246.6887   $246.69   $246.70   $246.70  
  Purchase #3 $114.42   11.470%   $127.544   $127.54   $127.55   $127.50  
  Purchase #4 $219.94   9.748%   $241.3798   $241.38   $241.40   $241.40  
  Purchase #5 $58.53   5.539%   $61.772   $61.77   $61.75   $61.80  
  Purchase #6 $178.41   10.440%   $197.036   $197.04   $197.05   $197.00  
  Purchase #7 $104.74   3.333%   $108.231   $108.23   $108.25   $108.20  
  7 purchase totals = $981.01       $1,065.6540   $1,065.65   $1,065.70   $1,065.60