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	$112.47	10.345%	$124.105	$124.11	$124.10	$124.10
Purchase #2	$105.43	9.635%	$115.5882	$115.59	$115.60	$115.60
Purchase #3	$111.78	10.236%	$123.2218	$123.22	$123.20	$123.20
Purchase #4	$73.44	12.305%	$82.4768	$82.48	$82.50	$82.50
Purchase #5	$102.54	9.176%	$111.9491	$111.95	$111.95	$111.90
Purchase #6	$48.91	6.392%	$52.0363	$52.04	$52.05	$52.00
Purchase #7	$25.63	11.736%	$28.6379	$28.64	$28.65	$28.60
7 purchase totals =	$580.20		$638.0151	$638.03	$638.05	$637.90