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 $116.86   8.461%   $126.7475   $126.75   $126.75   $126.70  
  Purchase #2 $36.54   3.408%   $37.7853   $37.79   $37.80   $37.80  
  Purchase #3 $233.32   8.117%   $252.2586   $252.26   $252.25   $252.30  
  Purchase #4 $36.99   11.134%   $41.1085   $41.11   $41.10   $41.10  
  Purchase #5 $58.86   4.204%   $61.3345   $61.33   $61.35   $61.30  
  Purchase #6 $113.74   13.564%   $129.1677   $129.17   $129.15   $129.20  
  Purchase #7 $249.87   7.667%   $269.0275   $269.03   $269.05   $269.00  
  7 purchase totals = $846.18       $917.4296   $917.44   $917.45   $917.40