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 $69.56   12.244%   $78.0769   $78.08   $78.10   $78.10  
  Purchase #2 $94.95   4.208%   $98.9455   $98.95   $98.95   $98.90  
  Purchase #3 $86.56   10.730%   $95.8479   $95.85   $95.85   $95.80  
  Purchase #4 $163.39   8.852%   $177.8533   $177.85   $177.85   $177.90  
  Purchase #5 $149.28   3.211%   $154.0734   $154.07   $154.05   $154.10  
  Purchase #6 $218.36   9.839%   $239.8444   $239.84   $239.85   $239.80  
  Purchase #7 $168.37   13.757%   $191.5327   $191.53   $191.55   $191.50  
  7 purchase totals = $950.47       $1,036.1741   $1,036.17   $1,036.20   $1,036.10