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	$193.92	13.140%	$219.4011	$219.40	$219.40	$219.40
Purchase #2	$6.41	13.726%	$7.2898	$7.29	$7.30	$7.30
Purchase #3	$78.92	12.201%	$88.549	$88.55	$88.55	$88.50
Purchase #4	$81.37	10.490%	$89.9057	$89.91	$89.90	$89.90
Purchase #5	$60.73	9.418%	$66.4496	$66.45	$66.45	$66.40
Purchase #6	$246.43	8.587%	$267.5909	$267.59	$267.60	$267.60
Purchase #7	$90.68	9.218%	$99.0389	$99.04	$99.05	$99.00
7 purchase totals =	$758.46		$838.2250	$838.23	$838.25	$838.10