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 $247.46   6.278%   $262.9955   $263.00   $263.00   $263.00  
  Purchase #2 $116.75   13.860%   $132.9316   $132.93   $132.95   $132.90  
  Purchase #3 $63.94   11.846%   $71.5143   $71.51   $71.50   $71.50  
  Purchase #4 $221.42   11.844%   $247.645   $247.65   $247.65   $247.60  
  Purchase #5 $122.55   4.139%   $127.6223   $127.62   $127.60   $127.60  
  Purchase #6 $141.61   10.246%   $156.1194   $156.12   $156.10   $156.10  
  Purchase #7 $199.40   13.782%   $226.8813   $226.88   $226.90   $226.90  
  7 purchase totals = $1,113.13       $1,225.7094   $1,225.71   $1,225.70   $1,225.60