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	$223.92	10.123%	$246.5874	$246.59	$246.60	$246.60
Purchase #2	$194.84	13.546%	$221.233	$221.23	$221.25	$221.20
Purchase #3	$162.89	13.191%	$184.3768	$184.38	$184.40	$184.40
Purchase #4	$23.78	7.509%	$25.5656	$25.57	$25.55	$25.60
Purchase #5	$35.86	12.616%	$40.3841	$40.38	$40.40	$40.40
Purchase #6	$27.56	13.137%	$31.1806	$31.18	$31.20	$31.20
Purchase #7	$82.49	11.150%	$91.6876	$91.69	$91.70	$91.70
7 purchase totals =	$751.34		$841.0151	$841.02	$841.10	$841.10