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	$38.41	6.367%	$40.8556	$40.86	$40.85	$40.90
Purchase #2	$131.87	3.557%	$136.5606	$136.56	$136.55	$136.60
Purchase #3	$164.51	4.143%	$171.3256	$171.33	$171.35	$171.30
Purchase #4	$226.76	3.722%	$235.2	$235.20	$235.20	$235.20
Purchase #5	$193.43	6.728%	$206.444	$206.44	$206.45	$206.40
Purchase #6	$131.73	6.130%	$139.805	$139.81	$139.80	$139.80
Purchase #7	$88.55	12.504%	$99.6223	$99.62	$99.60	$99.60
7 purchase totals =	$975.26		$1,029.8131	$1,029.82	$1,029.80	$1,029.80