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 $33.57   10.346%   $37.0432   $37.04   $37.05   $37.00  
  Purchase #2 $227.88   7.827%   $245.7162   $245.72   $245.70   $245.70  
  Purchase #3 $115.51   9.565%   $126.5585   $126.56   $126.55   $126.60  
  Purchase #4 $89.94   8.354%   $97.4536   $97.45   $97.45   $97.50  
  Purchase #5 $63.71   11.295%   $70.906   $70.91   $70.90   $70.90  
  Purchase #6 $36.78   10.325%   $40.5775   $40.58   $40.60   $40.60  
  Purchase #7 $226.55   4.596%   $236.9622   $236.96   $236.95   $237.00  
  7 purchase totals = $793.94       $855.2172   $855.22   $855.20   $855.30