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 $245.70   7.695%   $264.6066   $264.61   $264.60   $264.60  
  Purchase #2 $180.59   3.142%   $186.2641   $186.26   $186.25   $186.30  
  Purchase #3 $17.34   6.752%   $18.5108   $18.51   $18.50   $18.50  
  Purchase #4 $151.87   13.422%   $172.254   $172.25   $172.25   $172.30  
  Purchase #5 $70.34   6.860%   $75.1653   $75.17   $75.15   $75.20  
  Purchase #6 $179.99   8.483%   $195.2586   $195.26   $195.25   $195.30  
  Purchase #7 $107.64   9.237%   $117.5827   $117.58   $117.60   $117.60  
  7 purchase totals = $953.47       $1,029.6421   $1,029.64   $1,029.60   $1,029.80