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	$148.46	6.740%	$158.4662	$158.47	$158.45	$158.50
Purchase #2	$249.69	12.324%	$280.4618	$280.46	$280.45	$280.50
Purchase #3	$92.59	8.577%	$100.5314	$100.53	$100.55	$100.50
Purchase #4	$163.49	3.742%	$169.6078	$169.61	$169.60	$169.60
Purchase #5	$175.50	7.113%	$187.9833	$187.98	$188.00	$188.00
Purchase #6	$58.72	10.423%	$64.8404	$64.84	$64.85	$64.80
Purchase #7	$35.57	10.516%	$39.3105	$39.31	$39.30	$39.30
7 purchase totals =	$924.02		$1,001.2014	$1,001.20	$1,001.20	$1,001.20