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	$72.46	5.564%	$76.4917	$76.49	$76.50	$76.50
Purchase #2	$249.98	5.597%	$263.9714	$263.97	$263.95	$264.00
Purchase #3	$121.56	4.781%	$127.3718	$127.37	$127.35	$127.40
Purchase #4	$5.99	8.706%	$6.5115	$6.51	$6.50	$6.50
Purchase #5	$40.88	3.299%	$42.2286	$42.23	$42.25	$42.20
Purchase #6	$33.25	7.404%	$35.7118	$35.71	$35.70	$35.70
Purchase #7	$56.26	11.580%	$62.7749	$62.77	$62.75	$62.80
7 purchase totals =	$580.38		$615.0617	$615.05	$615.00	$615.10