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 $208.58   11.758%   $233.1048   $233.10   $233.10   $233.10  
  Purchase #2 $200.39   5.146%   $210.7021   $210.70   $210.70   $210.70  
  Purchase #3 $79.55   9.169%   $86.8439   $86.84   $86.85   $86.80  
  Purchase #4 $105.60   7.532%   $113.5538   $113.55   $113.55   $113.60  
  Purchase #5 $24.49   9.289%   $26.7649   $26.76   $26.75   $26.80  
  Purchase #6 $46.36   11.711%   $51.7892   $51.79   $51.80   $51.80  
  Purchase #7 $199.25   6.230%   $211.6633   $211.66   $211.65   $211.70  
  7 purchase totals = $864.22       $934.4220   $934.40   $934.40   $934.50