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	$39.94	5.486%	$42.1311	$42.13	$42.15	$42.10
Purchase #2	$227.38	13.110%	$257.1895	$257.19	$257.20	$257.20
Purchase #3	$141.89	13.363%	$160.8508	$160.85	$160.85	$160.90
Purchase #4	$156.37	11.564%	$174.4526	$174.45	$174.45	$174.50
Purchase #5	$93.61	8.817%	$101.8636	$101.86	$101.85	$101.90
Purchase #6	$223.93	6.494%	$238.472	$238.47	$238.45	$238.50
Purchase #7	$190.82	7.268%	$204.6888	$204.69	$204.70	$204.70
7 purchase totals =	$1,073.94		$1,179.6484	$1,179.64	$1,179.65	$1,179.80