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	$71.31	8.670%	$77.4926	$77.49	$77.50	$77.50
Purchase #2	$223.44	12.194%	$250.6863	$250.69	$250.70	$250.70
Purchase #3	$40.87	11.636%	$45.6256	$45.63	$45.65	$45.60
Purchase #4	$5.56	6.838%	$5.9402	$5.94	$5.95	$5.90
Purchase #5	$59.57	4.617%	$62.3203	$62.32	$62.30	$62.30
Purchase #6	$32.76	8.199%	$35.446	$35.45	$35.45	$35.40
Purchase #7	$16.59	12.773%	$18.709	$18.71	$18.70	$18.70
7 purchase totals =	$450.10		$496.2200	$496.23	$496.25	$496.10