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 $74.65   13.493%   $84.7225   $84.72   $84.70   $84.70  
  Purchase #2 $177.59   11.329%   $197.7092   $197.71   $197.70   $197.70  
  Purchase #3 $40.89   12.287%   $45.9142   $45.91   $45.90   $45.90  
  Purchase #4 $127.90   3.172%   $131.957   $131.96   $131.95   $132.00  
  Purchase #5 $218.65   9.393%   $239.1878   $239.19   $239.20   $239.20  
  Purchase #6 $163.54   13.761%   $186.0447   $186.04   $186.05   $186.00  
  Purchase #7 $219.72   13.678%   $249.7733   $249.77   $249.75   $249.80  
  7 purchase totals = $1,022.94       $1,135.3087   $1,135.30   $1,135.25   $1,135.30