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	$238.30	10.409%	$263.1046	$263.10	$263.10	$263.10
Purchase #2	$247.30	11.628%	$276.056	$276.06	$276.05	$276.10
Purchase #3	$246.54	6.319%	$262.1189	$262.12	$262.10	$262.10
Purchase #4	$49.87	6.518%	$53.1205	$53.12	$53.10	$53.10
Purchase #5	$184.33	3.573%	$190.9161	$190.92	$190.90	$190.90
Purchase #6	$105.59	9.799%	$115.9368	$115.94	$115.95	$115.90
Purchase #7	$92.77	11.435%	$103.3782	$103.38	$103.40	$103.40
7 purchase totals =	$1,164.70		$1,264.6311	$1,264.64	$1,264.60	$1,264.60