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 $22.91   11.802%   $25.6138   $25.61   $25.60   $25.60  
  Purchase #2 $246.51   9.118%   $268.9868   $268.99   $269.00   $269.00  
  Purchase #3 $240.86   10.223%   $265.4831   $265.48   $265.50   $265.50  
  Purchase #4 $42.63   12.779%   $48.0777   $48.08   $48.10   $48.10  
  Purchase #5 $154.80   4.273%   $161.4146   $161.41   $161.40   $161.40  
  Purchase #6 $145.53   5.825%   $154.0071   $154.01   $154.00   $154.00  
  Purchase #7 $173.70   3.813%   $180.3232   $180.32   $180.30   $180.30  
  7 purchase totals = $1,026.94       $1,103.9063   $1,103.90   $1,103.90   $1,103.90