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 $107.98   10.232%   $119.0285   $119.03   $119.05   $119.00  
  Purchase #2 $139.58   9.187%   $152.4032   $152.40   $152.40   $152.40  
  Purchase #3 $121.44   8.621%   $131.9093   $131.91   $131.90   $131.90  
  Purchase #4 $77.70   7.829%   $83.7831   $83.78   $83.80   $83.80  
  Purchase #5 $110.95   9.549%   $121.5446   $121.54   $121.55   $121.50  
  Purchase #6 $83.39   5.268%   $87.783   $87.78   $87.80   $87.80  
  Purchase #7 $78.49   5.279%   $82.6335   $82.63   $82.65   $82.60  
  7 purchase totals = $719.53       $779.0852   $779.07   $779.15   $779.00