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 $88.90   4.142%   $92.5822   $92.58   $92.60   $92.60  
  Purchase #2 $171.30   11.627%   $191.2171   $191.22   $191.20   $191.20  
  Purchase #3 $106.46   10.290%   $117.4147   $117.41   $117.40   $117.40  
  Purchase #4 $198.47   3.448%   $205.3132   $205.31   $205.30   $205.30  
  Purchase #5 $175.76   4.377%   $183.453   $183.45   $183.45   $183.50  
  Purchase #6 $5.86   9.540%   $6.419   $6.42   $6.40   $6.40  
  Purchase #7 $92.55   4.373%   $96.5972   $96.60   $96.60   $96.60  
  7 purchase totals = $839.30       $892.9964   $892.99   $892.95   $893.00