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	$215.31	8.398%	$233.3917	$233.39	$233.40	$233.40
Purchase #2	$165.63	4.109%	$172.4357	$172.44	$172.45	$172.40
Purchase #3	$245.55	7.483%	$263.9245	$263.92	$263.90	$263.90
Purchase #4	$98.92	12.593%	$111.377	$111.38	$111.40	$111.40
Purchase #5	$36.67	5.488%	$38.6824	$38.68	$38.70	$38.70
Purchase #6	$244.70	8.519%	$265.546	$265.55	$265.55	$265.50
Purchase #7	$222.91	4.266%	$232.4193	$232.42	$232.40	$232.40
7 purchase totals =	$1,229.69		$1,317.7766	$1,317.78	$1,317.80	$1,317.70