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	$39.95	4.862%	$41.8924	$41.89	$41.90	$41.90
Purchase #2	$26.54	6.752%	$28.332	$28.33	$28.35	$28.30
Purchase #3	$26.48	6.760%	$28.27	$28.27	$28.25	$28.30
Purchase #4	$242.86	7.405%	$260.8438	$260.84	$260.85	$260.80
Purchase #5	$214.66	3.565%	$222.3126	$222.31	$222.30	$222.30
Purchase #6	$159.25	13.586%	$180.8857	$180.89	$180.90	$180.90
Purchase #7	$8.81	12.103%	$9.8763	$9.88	$9.90	$9.90
7 purchase totals =	$718.55		$772.4128	$772.41	$772.45	$772.40