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	$242.82	8.330%	$263.0469	$263.05	$263.05	$263.00
Purchase #2	$93.89	10.491%	$103.74	$103.74	$103.75	$103.70
Purchase #3	$41.94	11.671%	$46.8348	$46.83	$46.85	$46.80
Purchase #4	$72.97	12.395%	$82.0146	$82.01	$82.00	$82.00
Purchase #5	$58.47	11.479%	$65.1818	$65.18	$65.20	$65.20
Purchase #6	$61.47	12.430%	$69.1107	$69.11	$69.10	$69.10
Purchase #7	$76.33	5.529%	$80.5503	$80.55	$80.55	$80.60
7 purchase totals =	$647.89		$710.4791	$710.47	$710.50	$710.40