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	$250.35	11.268%	$278.5594	$278.56	$278.55	$278.60
Purchase #2	$85.64	4.337%	$89.3542	$89.35	$89.35	$89.40
Purchase #3	$22.89	10.111%	$25.2044	$25.20	$25.20	$25.20
Purchase #4	$105.93	5.301%	$111.5453	$111.55	$111.55	$111.50
Purchase #5	$6.40	12.187%	$7.18	$7.18	$7.20	$7.20
Purchase #6	$133.27	4.514%	$139.2858	$139.29	$139.30	$139.30
Purchase #7	$135.84	12.527%	$152.8567	$152.86	$152.85	$152.90
7 purchase totals =	$740.32		$803.9858	$803.99	$804.00	$804.10