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 $182.70   10.751%   $202.3421   $202.34   $202.35   $202.30  
  Purchase #2 $20.43   9.249%   $22.3196   $22.32   $22.30   $22.30  
  Purchase #3 $195.44   3.866%   $202.9957   $203.00   $203.00   $203.00  
  Purchase #4 $230.83   6.691%   $246.2748   $246.27   $246.25   $246.30  
  Purchase #5 $21.97   13.340%   $24.9008   $24.90   $24.90   $24.90  
  Purchase #6 $25.32   8.316%   $27.4256   $27.43   $27.45   $27.40  
  Purchase #7 $224.73   10.487%   $248.2974   $248.30   $248.30   $248.30  
  7 purchase totals = $901.42       $974.5560   $974.56   $974.55   $974.50