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 $198.60   3.513%   $205.5768   $205.58   $205.60   $205.60  
  Purchase #2 $51.55   8.759%   $56.0653   $56.07   $56.05   $56.10  
  Purchase #3 $163.99   5.357%   $172.7749   $172.77   $172.75   $172.80  
  Purchase #4 $218.78   6.205%   $232.3553   $232.36   $232.35   $232.40  
  Purchase #5 $181.95   11.697%   $203.2327   $203.23   $203.25   $203.20  
  Purchase #6 $157.93   6.591%   $168.3392   $168.34   $168.35   $168.30  
  Purchase #7 $43.50   10.586%   $48.1049   $48.10   $48.10   $48.10  
  7 purchase totals = $1,016.30       $1,086.4491   $1,086.45   $1,086.45   $1,086.50