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	$246.91	13.636%	$280.5786	$280.58	$280.60	$280.60
Purchase #2	$65.33	3.538%	$67.6414	$67.64	$67.65	$67.60
Purchase #3	$150.26	13.346%	$170.3137	$170.31	$170.30	$170.30
Purchase #4	$90.63	9.776%	$99.49	$99.49	$99.50	$99.50
Purchase #5	$40.67	3.661%	$42.1589	$42.16	$42.15	$42.20
Purchase #6	$16.31	9.218%	$17.8135	$17.81	$17.80	$17.80
Purchase #7	$148.37	6.180%	$157.5393	$157.54	$157.55	$157.50
7 purchase totals =	$758.48		$835.5354	$835.53	$835.55	$835.50