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	$69.50	12.713%	$78.3355	$78.34	$78.35	$78.30
Purchase #2	$113.29	3.459%	$117.2087	$117.21	$117.20	$117.20
Purchase #3	$35.56	9.142%	$38.8109	$38.81	$38.80	$38.80
Purchase #4	$78.97	8.559%	$85.729	$85.73	$85.75	$85.70
Purchase #5	$171.67	13.134%	$194.2171	$194.22	$194.20	$194.20
Purchase #6	$223.69	8.447%	$242.5851	$242.59	$242.60	$242.60
Purchase #7	$144.26	4.622%	$150.9277	$150.93	$150.95	$150.90
7 purchase totals =	$836.94		$907.8140	$907.83	$907.85	$907.70