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 $88.76   7.498%   $95.4152   $95.42   $95.40   $95.40  
  Purchase #2 $131.58   10.720%   $145.6854   $145.69   $145.70   $145.70  
  Purchase #3 $171.74   3.680%   $178.06   $178.06   $178.05   $178.10  
  Purchase #4 $116.84   8.290%   $126.526   $126.53   $126.55   $126.50  
  Purchase #5 $183.99   9.152%   $200.8288   $200.83   $200.85   $200.80  
  Purchase #6 $43.87   10.143%   $48.3197   $48.32   $48.30   $48.30  
  Purchase #7 $67.93   7.616%   $73.1035   $73.10   $73.10   $73.10  
  7 purchase totals = $804.71       $867.9386   $867.95   $867.95   $867.90