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 $232.45   10.206%   $256.1738   $256.17   $256.15   $256.20  
  Purchase #2 $146.99   11.307%   $163.6102   $163.61   $163.60   $163.60  
  Purchase #3 $158.31   4.179%   $164.9258   $164.93   $164.95   $164.90  
  Purchase #4 $160.35   3.707%   $166.2942   $166.29   $166.30   $166.30  
  Purchase #5 $103.76   13.171%   $117.4262   $117.43   $117.45   $117.40  
  Purchase #6 $157.69   4.788%   $165.2402   $165.24   $165.25   $165.20  
  Purchase #7 $24.70   9.733%   $27.1041   $27.10   $27.10   $27.10  
  7 purchase totals = $984.25       $1,060.7745   $1,060.77   $1,060.80   $1,060.70