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 $56.49   6.194%   $59.989   $59.99   $60.00   $60.00  
  Purchase #2 $203.65   10.388%   $224.8052   $224.81   $224.80   $224.80  
  Purchase #3 $180.67   8.546%   $196.1101   $196.11   $196.10   $196.10  
  Purchase #4 $203.80   11.293%   $226.8151   $226.82   $226.80   $226.80  
  Purchase #5 $99.33   7.873%   $107.1503   $107.15   $107.15   $107.20  
  Purchase #6 $26.47   10.809%   $29.3311   $29.33   $29.35   $29.30  
  Purchase #7 $57.50   7.465%   $61.7924   $61.79   $61.80   $61.80  
  7 purchase totals = $827.91       $905.9932   $906.00   $906.00   $906.00