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 $179.67   7.792%   $193.6699   $193.67   $193.65   $193.70  
  Purchase #2 $170.96   9.119%   $186.5498   $186.55   $186.55   $186.50  
  Purchase #3 $48.50   13.106%   $54.8564   $54.86   $54.85   $54.90  
  Purchase #4 $47.32   8.718%   $51.4454   $51.45   $51.45   $51.40  
  Purchase #5 $199.37   4.756%   $208.852   $208.85   $208.85   $208.90  
  Purchase #6 $33.89   8.260%   $36.6893   $36.69   $36.70   $36.70  
  Purchase #7 $86.79   5.260%   $91.3552   $91.36   $91.35   $91.40  
  7 purchase totals = $766.50       $823.4180   $823.43   $823.40   $823.50