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 $187.56   8.198%   $202.9362   $202.94   $202.95   $202.90  
  Purchase #2 $123.93   7.565%   $133.3053   $133.31   $133.30   $133.30  
  Purchase #3 $189.65   10.116%   $208.835   $208.84   $208.85   $208.80  
  Purchase #4 $51.74   8.677%   $56.2295   $56.23   $56.25   $56.20  
  Purchase #5 $48.54   6.644%   $51.765   $51.77   $51.75   $51.80  
  Purchase #6 $97.87   9.854%   $107.5141   $107.51   $107.50   $107.50  
  Purchase #7 $147.57   7.642%   $158.8473   $158.85   $158.85   $158.80  
  7 purchase totals = $846.86       $919.4324   $919.45   $919.45   $919.30