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	$208.50	4.854%	$218.6206	$218.62	$218.60	$218.60
Purchase #2	$89.88	12.235%	$100.8768	$100.88	$100.90	$100.90
Purchase #3	$234.79	8.424%	$254.5687	$254.57	$254.55	$254.60
Purchase #4	$39.97	12.592%	$45.003	$45.00	$45.00	$45.00
Purchase #5	$19.96	3.848%	$20.7281	$20.73	$20.75	$20.70
Purchase #6	$20.96	4.549%	$21.9135	$21.91	$21.90	$21.90
Purchase #7	$136.48	12.474%	$153.5045	$153.50	$153.50	$153.50
7 purchase totals =	$750.54		$815.2152	$815.21	$815.20	$815.20