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	$43.38	4.766%	$45.4475	$45.45	$45.45	$45.40
Purchase #2	$121.62	3.506%	$125.884	$125.88	$125.90	$125.90
Purchase #3	$136.86	12.702%	$154.244	$154.24	$154.25	$154.20
Purchase #4	$115.91	4.340%	$120.9405	$120.94	$120.95	$120.90
Purchase #5	$35.62	13.408%	$40.3959	$40.40	$40.40	$40.40
Purchase #6	$71.52	12.298%	$80.3155	$80.32	$80.30	$80.30
Purchase #7	$46.41	11.541%	$51.7662	$51.77	$51.75	$51.80
7 purchase totals =	$571.32		$618.9936	$619.00	$619.00	$618.90