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 $202.43   11.666%   $226.0455   $226.05   $226.05   $226.00  
  Purchase #2 $74.79   4.356%   $78.0479   $78.05   $78.05   $78.00  
  Purchase #3 $190.78   5.268%   $200.8303   $200.83   $200.85   $200.80  
  Purchase #4 $68.70   7.578%   $73.9061   $73.91   $73.90   $73.90  
  Purchase #5 $60.97   13.631%   $69.2808   $69.28   $69.30   $69.30  
  Purchase #6 $185.93   6.838%   $198.6439   $198.64   $198.65   $198.60  
  Purchase #7 $200.92   7.169%   $215.324   $215.32   $215.30   $215.30  
  7 purchase totals = $984.52       $1,062.0785   $1,062.08   $1,062.10   $1,061.90