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 $74.47   11.453%   $82.999   $83.00   $83.00   $83.00  
  Purchase #2 $130.92   6.698%   $139.689   $139.69   $139.70   $139.70  
  Purchase #3 $162.92   11.742%   $182.0501   $182.05   $182.05   $182.10  
  Purchase #4 $60.58   9.195%   $66.1503   $66.15   $66.15   $66.20  
  Purchase #5 $187.99   11.208%   $209.0599   $209.06   $209.05   $209.10  
  Purchase #6 $130.59   11.733%   $145.9121   $145.91   $145.90   $145.90  
  Purchase #7 $184.88   8.302%   $200.2287   $200.23   $200.25   $200.20  
  7 purchase totals = $932.35       $1,026.0891   $1,026.09   $1,026.10   $1,026.20