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	$133.83	5.301%	$140.9243	$140.92	$140.90	$140.90
Purchase #2	$125.79	5.818%	$133.1085	$133.11	$133.10	$133.10
Purchase #3	$163.67	13.619%	$185.9602	$185.96	$185.95	$186.00
Purchase #4	$154.40	8.573%	$167.6367	$167.64	$167.65	$167.60
Purchase #5	$37.89	5.717%	$40.0562	$40.06	$40.05	$40.10
Purchase #6	$38.73	13.160%	$43.8269	$43.83	$43.85	$43.80
Purchase #7	$88.52	3.510%	$91.6271	$91.63	$91.65	$91.60
7 purchase totals =	$742.83		$803.1399	$803.15	$803.15	$803.10