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 $59.41   7.428%   $63.823   $63.82   $63.80   $63.80  
  Purchase #2 $249.85   8.696%   $271.577   $271.58   $271.60   $271.60  
  Purchase #3 $13.90   5.523%   $14.6677   $14.67   $14.65   $14.70  
  Purchase #4 $192.40   3.868%   $199.842   $199.84   $199.85   $199.80  
  Purchase #5 $32.42   12.483%   $36.467   $36.47   $36.45   $36.50  
  Purchase #6 $207.74   6.359%   $220.9502   $220.95   $220.95   $221.00  
  Purchase #7 $175.87   3.724%   $182.4194   $182.42   $182.40   $182.40  
  7 purchase totals = $931.59       $989.7463   $989.75   $989.70   $989.80