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 $216.32   8.313%   $234.3027   $234.30   $234.30   $234.30  
  Purchase #2 $141.90   7.758%   $152.9086   $152.91   $152.90   $152.90  
  Purchase #3 $44.55   11.358%   $49.61   $49.61   $49.60   $49.60  
  Purchase #4 $40.69   6.282%   $43.2461   $43.25   $43.25   $43.20  
  Purchase #5 $236.93   13.732%   $269.4652   $269.47   $269.45   $269.50  
  Purchase #6 $198.60   5.512%   $209.5468   $209.55   $209.55   $209.50  
  Purchase #7 $150.34   8.799%   $163.5684   $163.57   $163.55   $163.60  
  7 purchase totals = $1,029.33       $1,122.6478   $1,122.66   $1,122.60   $1,122.60