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	$195.98	7.450%	$210.5805	$210.58	$210.60	$210.60
Purchase #2	$243.85	4.701%	$255.3134	$255.31	$255.30	$255.30
Purchase #3	$173.97	13.498%	$197.4525	$197.45	$197.45	$197.50
Purchase #4	$184.48	5.419%	$194.477	$194.48	$194.50	$194.50
Purchase #5	$65.46	9.199%	$71.4817	$71.48	$71.50	$71.50
Purchase #6	$37.26	10.152%	$41.0426	$41.04	$41.05	$41.00
Purchase #7	$25.31	12.421%	$28.4538	$28.45	$28.45	$28.50
7 purchase totals =	$926.31		$998.8015	$998.79	$998.85	$998.90