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	$36.92	10.468%	$40.7848	$40.78	$40.80	$40.80
Purchase #2	$161.54	6.335%	$171.7736	$171.77	$171.75	$171.80
Purchase #3	$44.50	3.713%	$46.1523	$46.15	$46.15	$46.20
Purchase #4	$200.67	5.717%	$212.1423	$212.14	$212.15	$212.10
Purchase #5	$99.81	3.316%	$103.1197	$103.12	$103.10	$103.10
Purchase #6	$13.73	5.410%	$14.4728	$14.47	$14.45	$14.50
Purchase #7	$233.42	12.632%	$262.9056	$262.91	$262.90	$262.90
7 purchase totals =	$790.59		$851.3511	$851.34	$851.30	$851.40