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 $76.25   12.262%   $85.5998   $85.60   $85.60   $85.60  
  Purchase #2 $224.85   6.444%   $239.3393   $239.34   $239.35   $239.30  
  Purchase #3 $122.72   11.821%   $137.2267   $137.23   $137.25   $137.20  
  Purchase #4 $139.29   8.445%   $151.053   $151.05   $151.05   $151.10  
  Purchase #5 $247.40   11.573%   $276.0316   $276.03   $276.05   $276.00  
  Purchase #6 $202.51   5.194%   $213.0284   $213.03   $213.05   $213.00  
  Purchase #7 $117.95   12.192%   $132.3305   $132.33   $132.35   $132.30  
  7 purchase totals = $1,130.97       $1,234.6093   $1,234.61   $1,234.70   $1,234.50