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	$34.65	7.727%	$37.3274	$37.33	$37.35	$37.30
Purchase #2	$148.71	3.755%	$154.2941	$154.29	$154.30	$154.30
Purchase #3	$98.66	4.175%	$102.7791	$102.78	$102.80	$102.80
Purchase #4	$154.70	11.722%	$172.8339	$172.83	$172.85	$172.80
Purchase #5	$50.58	8.280%	$54.768	$54.77	$54.75	$54.80
Purchase #6	$137.58	3.465%	$142.3471	$142.35	$142.35	$142.30
Purchase #7	$20.62	8.479%	$22.3684	$22.37	$22.35	$22.40
7 purchase totals =	$645.50		$686.7180	$686.72	$686.75	$686.70