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 $7.92   10.594%   $8.759   $8.76   $8.75   $8.80  
  Purchase #2 $30.80   11.596%   $34.3716   $34.37   $34.35   $34.40  
  Purchase #3 $175.68   13.733%   $199.8061   $199.81   $199.80   $199.80  
  Purchase #4 $246.70   7.460%   $265.1038   $265.10   $265.10   $265.10  
  Purchase #5 $210.64   8.284%   $228.0894   $228.09   $228.10   $228.10  
  Purchase #6 $147.81   8.170%   $159.8861   $159.89   $159.90   $159.90  
  Purchase #7 $229.81   4.534%   $240.2296   $240.23   $240.25   $240.20  
  7 purchase totals = $1,049.36       $1,136.2456   $1,136.25   $1,136.25   $1,136.30