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	$114.86	3.286%	$118.6343	$118.63	$118.65	$118.60
Purchase #2	$242.47	12.106%	$271.8234	$271.82	$271.80	$271.80
Purchase #3	$51.96	13.556%	$59.0037	$59.00	$59.00	$59.00
Purchase #4	$155.61	12.516%	$175.0861	$175.09	$175.10	$175.10
Purchase #5	$172.30	7.171%	$184.6556	$184.66	$184.65	$184.70
Purchase #6	$40.83	5.595%	$43.1144	$43.11	$43.10	$43.10
Purchase #7	$110.82	7.468%	$119.096	$119.10	$119.10	$119.10
7 purchase totals =	$888.85		$971.4135	$971.41	$971.40	$971.40