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	$212.89	13.860%	$242.3966	$242.40	$242.40	$242.40
Purchase #2	$153.29	11.291%	$170.598	$170.60	$170.60	$170.60
Purchase #3	$45.81	13.207%	$51.8601	$51.86	$51.85	$51.90
Purchase #4	$115.70	10.216%	$127.5199	$127.52	$127.50	$127.50
Purchase #5	$95.56	6.272%	$101.5535	$101.55	$101.55	$101.60
Purchase #6	$88.50	10.597%	$97.8783	$97.88	$97.90	$97.90
Purchase #7	$233.41	11.703%	$260.726	$260.73	$260.75	$260.70
7 purchase totals =	$945.16		$1,052.5324	$1,052.54	$1,052.55	$1,052.60