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 $81.41   13.816%   $92.6576   $92.66   $92.65   $92.70  
  Purchase #2 $43.73   6.321%   $46.4942   $46.49   $46.50   $46.50  
  Purchase #3 $115.81   11.274%   $128.8664   $128.87   $128.85   $128.90  
  Purchase #4 $24.49   10.723%   $27.1161   $27.12   $27.10   $27.10  
  Purchase #5 $170.29   3.280%   $175.8755   $175.88   $175.90   $175.90  
  Purchase #6 $219.69   13.247%   $248.7923   $248.79   $248.80   $248.80  
  Purchase #7 $240.79   10.472%   $266.0055   $266.01   $266.00   $266.00  
  7 purchase totals = $896.21       $985.8076   $985.82   $985.80   $985.90