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 $225.91   9.327%   $246.9806   $246.98   $247.00   $247.00  
  Purchase #2 $181.95   8.734%   $197.8415   $197.84   $197.85   $197.80  
  Purchase #3 $111.69   10.231%   $123.117   $123.12   $123.10   $123.10  
  Purchase #4 $14.90   3.725%   $15.455   $15.46   $15.45   $15.50  
  Purchase #5 $103.91   5.556%   $109.6832   $109.68   $109.70   $109.70  
  Purchase #6 $143.94   13.567%   $163.4683   $163.47   $163.45   $163.50  
  Purchase #7 $150.33   9.482%   $164.5843   $164.58   $164.60   $164.60  
  7 purchase totals = $932.63       $1,021.1299   $1,021.13   $1,021.15   $1,021.20