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	$72.98	6.701%	$77.8704	$77.87	$77.85	$77.90
Purchase #2	$180.44	8.562%	$195.8893	$195.89	$195.90	$195.90
Purchase #3	$219.96	13.110%	$248.7968	$248.80	$248.80	$248.80
Purchase #4	$165.58	4.265%	$172.642	$172.64	$172.65	$172.60
Purchase #5	$56.57	5.576%	$59.7243	$59.72	$59.70	$59.70
Purchase #6	$172.38	7.665%	$185.5929	$185.59	$185.60	$185.60
Purchase #7	$247.41	13.386%	$280.5283	$280.53	$280.55	$280.50
7 purchase totals =	$1,115.32		$1,221.0440	$1,221.04	$1,221.05	$1,221.00