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 $83.58   10.202%   $92.1068   $92.11   $92.10   $92.10  
  Purchase #2 $159.86   7.767%   $172.2763   $172.28   $172.30   $172.30  
  Purchase #3 $51.40   5.859%   $54.4115   $54.41   $54.40   $54.40  
  Purchase #4 $97.81   9.385%   $106.9895   $106.99   $107.00   $107.00  
  Purchase #5 $229.66   4.481%   $239.9511   $239.95   $239.95   $240.00  
  Purchase #6 $181.87   13.515%   $206.4497   $206.45   $206.45   $206.40  
  Purchase #7 $69.34   12.608%   $78.0824   $78.08   $78.10   $78.10  
  7 purchase totals = $873.52       $950.2673   $950.27   $950.30   $950.30