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	$210.50	13.121%	$238.1197	$238.12	$238.10	$238.10
Purchase #2	$39.73	3.164%	$40.9871	$40.99	$41.00	$41.00
Purchase #3	$195.59	8.824%	$212.8489	$212.85	$212.85	$212.80
Purchase #4	$39.89	13.160%	$45.1395	$45.14	$45.15	$45.10
Purchase #5	$129.40	3.481%	$133.9044	$133.90	$133.90	$133.90
Purchase #6	$67.60	4.757%	$70.8157	$70.82	$70.80	$70.80
Purchase #7	$94.83	4.339%	$98.9447	$98.94	$98.95	$98.90
7 purchase totals =	$777.54		$840.7600	$840.76	$840.75	$840.60