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	$47.93	4.788%	$50.2249	$50.22	$50.20	$50.20
Purchase #2	$249.52	12.221%	$280.0138	$280.01	$280.00	$280.00
Purchase #3	$190.31	13.856%	$216.6794	$216.68	$216.70	$216.70
Purchase #4	$247.42	6.715%	$264.0343	$264.03	$264.05	$264.00
Purchase #5	$7.72	5.783%	$8.1664	$8.17	$8.15	$8.20
Purchase #6	$99.75	5.383%	$105.1195	$105.12	$105.10	$105.10
Purchase #7	$149.57	12.662%	$168.5086	$168.51	$168.50	$168.50
7 purchase totals =	$992.22		$1,092.7469	$1,092.74	$1,092.70	$1,092.70