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 $209.96   10.526%   $232.0604   $232.06   $232.05   $232.10  
  Purchase #2 $220.98   6.593%   $235.5492   $235.55   $235.55   $235.50  
  Purchase #3 $101.99   12.448%   $114.6857   $114.69   $114.70   $114.70  
  Purchase #4 $182.69   5.320%   $192.4091   $192.41   $192.40   $192.40  
  Purchase #5 $247.42   12.725%   $278.9042   $278.90   $278.90   $278.90  
  Purchase #6 $243.25   4.744%   $254.7898   $254.79   $254.80   $254.80  
  Purchase #7 $158.71   4.437%   $165.752   $165.75   $165.75   $165.80  
  7 purchase totals = $1,365.00       $1,474.1504   $1,474.15   $1,474.15   $1,474.20