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	$205.96	8.684%	$223.8456	$223.85	$223.85	$223.80
Purchase #2	$180.52	4.606%	$188.8348	$188.83	$188.85	$188.80
Purchase #3	$246.49	11.139%	$273.9465	$273.95	$273.95	$273.90
Purchase #4	$33.98	3.281%	$35.0949	$35.09	$35.10	$35.10
Purchase #5	$191.28	11.837%	$213.9218	$213.92	$213.90	$213.90
Purchase #6	$114.63	10.796%	$127.0055	$127.01	$127.00	$127.00
Purchase #7	$57.41	13.865%	$65.3699	$65.37	$65.35	$65.40
7 purchase totals =	$1,030.27		$1,128.0190	$1,128.02	$1,128.00	$1,127.90