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 $96.95   10.417%   $107.0493   $107.05   $107.05   $107.00  
  Purchase #2 $8.34   12.150%   $9.3533   $9.35   $9.35   $9.40  
  Purchase #3 $237.30   11.602%   $264.8315   $264.83   $264.85   $264.80  
  Purchase #4 $94.75   3.537%   $98.1013   $98.10   $98.10   $98.10  
  Purchase #5 $234.70   8.193%   $253.929   $253.93   $253.95   $253.90  
  Purchase #6 $158.73   8.807%   $172.7094   $172.71   $172.70   $172.70  
  Purchase #7 $103.60   4.493%   $108.2547   $108.25   $108.25   $108.30  
  7 purchase totals = $934.37       $1,014.2285   $1,014.22   $1,014.25   $1,014.20