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	$150.34	9.790%	$165.0583	$165.06	$165.05	$165.10
Purchase #2	$41.64	7.839%	$44.9042	$44.90	$44.90	$44.90
Purchase #3	$109.95	3.386%	$113.6729	$113.67	$113.65	$113.70
Purchase #4	$85.91	12.248%	$96.4323	$96.43	$96.45	$96.40
Purchase #5	$127.79	11.106%	$141.9824	$141.98	$142.00	$142.00
Purchase #6	$149.46	4.527%	$156.2261	$156.23	$156.25	$156.20
Purchase #7	$142.89	10.114%	$157.3419	$157.34	$157.35	$157.30
7 purchase totals =	$807.98		$875.6181	$875.61	$875.65	$875.60