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 $69.36   13.839%   $78.9587   $78.96   $78.95   $79.00  
  Purchase #2 $166.62   6.686%   $177.7602   $177.76   $177.75   $177.80  
  Purchase #3 $157.32   7.338%   $168.8641   $168.86   $168.85   $168.90  
  Purchase #4 $202.78   7.154%   $217.2869   $217.29   $217.30   $217.30  
  Purchase #5 $189.62   10.243%   $209.0428   $209.04   $209.05   $209.00  
  Purchase #6 $220.60   13.405%   $250.1714   $250.17   $250.15   $250.20  
  Purchase #7 $49.61   6.750%   $52.9587   $52.96   $52.95   $53.00  
  7 purchase totals = $1,055.91       $1,155.0428   $1,155.04   $1,155.00   $1,155.20