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 $208.66   12.188%   $234.0915   $234.09   $234.10   $234.10  
  Purchase #2 $65.92   10.759%   $73.0123   $73.01   $73.00   $73.00  
  Purchase #3 $224.64   11.643%   $250.7948   $250.79   $250.80   $250.80  
  Purchase #4 $90.59   4.320%   $94.5035   $94.50   $94.50   $94.50  
  Purchase #5 $233.66   11.697%   $260.9912   $260.99   $261.00   $261.00  
  Purchase #6 $59.94   12.335%   $67.3336   $67.33   $67.35   $67.30  
  Purchase #7 $115.87   9.740%   $127.1557   $127.16   $127.15   $127.20  
  7 purchase totals = $999.28       $1,107.8826   $1,107.87   $1,107.90   $1,107.90