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	$123.57	4.164%	$128.7155	$128.72	$128.70	$128.70
Purchase #2	$229.56	8.431%	$248.9142	$248.91	$248.90	$248.90
Purchase #3	$213.99	4.107%	$222.7786	$222.78	$222.80	$222.80
Purchase #4	$166.72	6.499%	$177.5551	$177.56	$177.55	$177.60
Purchase #5	$107.37	3.610%	$111.2461	$111.25	$111.25	$111.20
Purchase #6	$228.59	6.504%	$243.4575	$243.46	$243.45	$243.50
Purchase #7	$20.89	5.668%	$22.074	$22.07	$22.05	$22.10
7 purchase totals =	$1,090.69		$1,154.7410	$1,154.75	$1,154.70	$1,154.80