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	$14.41	13.874%	$16.4092	$16.41	$16.40	$16.40
Purchase #2	$210.62	9.210%	$230.0181	$230.02	$230.00	$230.00
Purchase #3	$122.82	4.404%	$128.229	$128.23	$128.25	$128.20
Purchase #4	$20.55	6.740%	$21.9351	$21.94	$21.95	$21.90
Purchase #5	$127.50	9.755%	$139.9376	$139.94	$139.95	$139.90
Purchase #6	$130.30	12.458%	$146.5328	$146.53	$146.55	$146.50
Purchase #7	$81.75	9.282%	$89.338	$89.34	$89.35	$89.30
7 purchase totals =	$707.95		$772.3998	$772.41	$772.45	$772.20