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	$97.26	10.331%	$107.3079	$107.31	$107.30	$107.30
Purchase #2	$230.72	4.250%	$240.5256	$240.53	$240.55	$240.50
Purchase #3	$221.57	5.527%	$233.8162	$233.82	$233.80	$233.80
Purchase #4	$218.50	11.798%	$244.2786	$244.28	$244.30	$244.30
Purchase #5	$248.39	10.600%	$274.7193	$274.72	$274.70	$274.70
Purchase #6	$88.31	12.469%	$99.3214	$99.32	$99.30	$99.30
Purchase #7	$211.61	10.376%	$233.5667	$233.57	$233.55	$233.60
7 purchase totals =	$1,316.36		$1,433.5357	$1,433.55	$1,433.50	$1,433.50