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 $239.34   8.424%   $259.502   $259.50   $259.50   $259.50  
  Purchase #2 $86.96   12.610%   $97.9257   $97.93   $97.95   $97.90  
  Purchase #3 $67.40   10.521%   $74.4912   $74.49   $74.50   $74.50  
  Purchase #4 $66.72   12.113%   $74.8018   $74.80   $74.80   $74.80  
  Purchase #5 $199.43   11.779%   $222.9209   $222.92   $222.90   $222.90  
  Purchase #6 $61.61   3.822%   $63.9647   $63.96   $63.95   $64.00  
  Purchase #7 $240.99   7.145%   $258.2087   $258.21   $258.20   $258.20  
  7 purchase totals = $962.45       $1,051.8150   $1,051.81   $1,051.80   $1,051.80