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 $44.79   3.833%   $46.5068   $46.51   $46.50   $46.50  
  Purchase #2 $134.95   13.761%   $153.5205   $153.52   $153.50   $153.50  
  Purchase #3 $142.33   3.511%   $147.3272   $147.33   $147.35   $147.30  
  Purchase #4 $241.29   4.223%   $251.4797   $251.48   $251.50   $251.50  
  Purchase #5 $163.36   8.312%   $176.9385   $176.94   $176.95   $176.90  
  Purchase #6 $208.26   9.230%   $227.4824   $227.48   $227.50   $227.50  
  Purchase #7 $200.54   12.853%   $226.3154   $226.32   $226.30   $226.30  
  7 purchase totals = $1,135.52       $1,229.5705   $1,229.58   $1,229.60   $1,229.50