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 $89.66   7.491%   $96.3764   $96.38   $96.40   $96.40  
  Purchase #2 $95.61   5.395%   $100.7682   $100.77   $100.75   $100.80  
  Purchase #3 $8.50   5.767%   $8.9902   $8.99   $9.00   $9.00  
  Purchase #4 $203.60   11.855%   $227.7368   $227.74   $227.75   $227.70  
  Purchase #5 $107.91   7.588%   $116.0982   $116.10   $116.10   $116.10  
  Purchase #6 $207.30   11.633%   $231.4152   $231.42   $231.40   $231.40  
  Purchase #7 $155.87   8.203%   $168.656   $168.66   $168.65   $168.70  
  7 purchase totals = $868.45       $950.0410   $950.06   $950.05   $950.10