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	$127.29	5.371%	$134.1267	$134.13	$134.15	$134.10
Purchase #2	$73.64	11.440%	$82.0644	$82.06	$82.05	$82.10
Purchase #3	$94.49	9.680%	$103.6366	$103.64	$103.65	$103.60
Purchase #4	$48.98	11.386%	$54.5569	$54.56	$54.55	$54.60
Purchase #5	$28.55	11.385%	$31.8004	$31.80	$31.80	$31.80
Purchase #6	$229.25	9.510%	$251.0517	$251.05	$251.05	$251.10
Purchase #7	$159.45	7.709%	$171.742	$171.74	$171.75	$171.70
7 purchase totals =	$761.65		$828.9787	$828.98	$829.00	$829.00