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	$119.91	13.644%	$136.2705	$136.27	$136.25	$136.30
Purchase #2	$33.54	6.401%	$35.6869	$35.69	$35.70	$35.70
Purchase #3	$216.79	7.256%	$232.5203	$232.52	$232.50	$232.50
Purchase #4	$80.47	12.316%	$90.3807	$90.38	$90.40	$90.40
Purchase #5	$165.43	13.353%	$187.5199	$187.52	$187.50	$187.50
Purchase #6	$194.98	4.492%	$203.7385	$203.74	$203.75	$203.70
Purchase #7	$132.70	13.231%	$150.2575	$150.26	$150.25	$150.30
7 purchase totals =	$943.82		$1,036.3743	$1,036.38	$1,036.35	$1,036.40