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	$34.94	9.673%	$38.3197	$38.32	$38.30	$38.30
Purchase #2	$36.98	10.669%	$40.9254	$40.93	$40.95	$40.90
Purchase #3	$234.41	3.141%	$241.7728	$241.77	$241.75	$241.80
Purchase #4	$238.80	4.815%	$250.2982	$250.30	$250.30	$250.30
Purchase #5	$178.26	10.388%	$196.7776	$196.78	$196.80	$196.80
Purchase #6	$236.62	7.733%	$254.9178	$254.92	$254.90	$254.90
Purchase #7	$159.54	5.445%	$168.227	$168.23	$168.25	$168.20
7 purchase totals =	$1,119.55		$1,191.2385	$1,191.25	$1,191.25	$1,191.20