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 $205.26   10.523%   $226.8595   $226.86   $226.85   $226.90  
  Purchase #2 $49.94   7.483%   $53.677   $53.68   $53.70   $53.70  
  Purchase #3 $100.75   5.453%   $106.2439   $106.24   $106.25   $106.20  
  Purchase #4 $61.45   5.659%   $64.9275   $64.93   $64.95   $64.90  
  Purchase #5 $202.63   4.431%   $211.6085   $211.61   $211.60   $211.60  
  Purchase #6 $58.59   8.674%   $63.6721   $63.67   $63.65   $63.70  
  Purchase #7 $169.83   13.518%   $192.7876   $192.79   $192.80   $192.80  
  7 purchase totals = $848.45       $919.7761   $919.78   $919.80   $919.80