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	$96.61	3.844%	$100.3237	$100.32	$100.30	$100.30
Purchase #2	$36.95	9.624%	$40.5061	$40.51	$40.50	$40.50
Purchase #3	$157.95	13.793%	$179.736	$179.74	$179.75	$179.70
Purchase #4	$229.84	10.575%	$254.1456	$254.15	$254.15	$254.10
Purchase #5	$103.62	9.377%	$113.3364	$113.34	$113.35	$113.30
Purchase #6	$33.34	13.235%	$37.7525	$37.75	$37.75	$37.80
Purchase #7	$215.99	3.490%	$223.5281	$223.53	$223.55	$223.50
7 purchase totals =	$874.30		$949.3284	$949.34	$949.35	$949.20