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 $222.87   7.365%   $239.2844   $239.28   $239.30   $239.30  
  Purchase #2 $169.94   13.349%   $192.6253   $192.63   $192.65   $192.60  
  Purchase #3 $44.46   4.716%   $46.5567   $46.56   $46.55   $46.60  
  Purchase #4 $109.59   9.279%   $119.7589   $119.76   $119.75   $119.80  
  Purchase #5 $119.63   9.466%   $130.9542   $130.95   $130.95   $131.00  
  Purchase #6 $49.28   6.724%   $52.5936   $52.59   $52.60   $52.60  
  Purchase #7 $170.80   4.688%   $178.8071   $178.81   $178.80   $178.80  
  7 purchase totals = $886.57       $960.5802   $960.58   $960.60   $960.70