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	$18.54	8.297%	$20.0783	$20.08	$20.10	$20.10
Purchase #2	$245.56	11.601%	$274.0474	$274.05	$274.05	$274.00
Purchase #3	$93.62	7.718%	$100.8456	$100.85	$100.85	$100.80
Purchase #4	$237.88	5.416%	$250.7636	$250.76	$250.75	$250.80
Purchase #5	$72.86	3.352%	$75.3023	$75.30	$75.30	$75.30
Purchase #6	$120.81	5.531%	$127.492	$127.49	$127.50	$127.50
Purchase #7	$184.89	6.436%	$196.7895	$196.79	$196.80	$196.80
7 purchase totals =	$974.16		$1,045.3187	$1,045.32	$1,045.35	$1,045.30