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	$229.59	3.843%	$238.4131	$238.41	$238.40	$238.40
Purchase #2	$31.93	5.666%	$33.7392	$33.74	$33.75	$33.70
Purchase #3	$42.75	3.330%	$44.1736	$44.17	$44.15	$44.20
Purchase #4	$223.38	6.862%	$238.7083	$238.71	$238.70	$238.70
Purchase #5	$79.83	8.104%	$86.2994	$86.30	$86.30	$86.30
Purchase #6	$129.96	10.701%	$143.867	$143.87	$143.85	$143.90
Purchase #7	$99.70	5.453%	$105.1366	$105.14	$105.15	$105.10
7 purchase totals =	$837.14		$890.3372	$890.34	$890.30	$890.30