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	$35.45	6.579%	$37.7823	$37.78	$37.80	$37.80
Purchase #2	$127.59	12.618%	$143.6893	$143.69	$143.70	$143.70
Purchase #3	$122.79	5.836%	$129.956	$129.96	$129.95	$130.00
Purchase #4	$198.51	12.449%	$223.2225	$223.22	$223.20	$223.20
Purchase #5	$145.89	11.430%	$162.5652	$162.57	$162.55	$162.60
Purchase #6	$25.54	11.240%	$28.4107	$28.41	$28.40	$28.40
Purchase #7	$70.51	5.693%	$74.5241	$74.52	$74.50	$74.50
7 purchase totals =	$726.28		$800.1501	$800.15	$800.10	$800.20