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	$145.89	6.181%	$154.9075	$154.91	$154.90	$154.90
Purchase #2	$238.48	10.599%	$263.7565	$263.76	$263.75	$263.80
Purchase #3	$148.56	7.258%	$159.3425	$159.34	$159.35	$159.30
Purchase #4	$35.92	13.873%	$40.9032	$40.90	$40.90	$40.90
Purchase #5	$188.83	6.353%	$200.8264	$200.83	$200.85	$200.80
Purchase #6	$163.72	4.806%	$171.5884	$171.59	$171.60	$171.60
Purchase #7	$103.59	8.788%	$112.6935	$112.69	$112.70	$112.70
7 purchase totals =	$1,024.99		$1,104.0180	$1,104.02	$1,104.05	$1,104.00