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	$135.69	9.767%	$148.9428	$148.94	$148.95	$148.90
Purchase #2	$35.78	4.436%	$37.3672	$37.37	$37.35	$37.40
Purchase #3	$23.76	6.372%	$25.274	$25.27	$25.25	$25.30
Purchase #4	$223.68	4.743%	$234.2891	$234.29	$234.30	$234.30
Purchase #5	$35.85	7.609%	$38.5778	$38.58	$38.60	$38.60
Purchase #6	$74.82	12.148%	$83.9091	$83.91	$83.90	$83.90
Purchase #7	$66.90	8.216%	$72.3965	$72.40	$72.40	$72.40
7 purchase totals =	$596.48		$640.7565	$640.76	$640.75	$640.80