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	$43.39	3.831%	$45.0523	$45.05	$45.05	$45.10
Purchase #2	$137.77	7.261%	$147.7735	$147.77	$147.75	$147.80
Purchase #3	$78.32	12.758%	$88.3121	$88.31	$88.30	$88.30
Purchase #4	$59.51	5.131%	$62.5635	$62.56	$62.55	$62.60
Purchase #5	$83.84	13.466%	$95.1299	$95.13	$95.15	$95.10
Purchase #6	$145.33	6.376%	$154.5962	$154.60	$154.60	$154.60
Purchase #7	$73.76	3.445%	$76.301	$76.30	$76.30	$76.30
7 purchase totals =	$621.92		$669.7285	$669.72	$669.70	$669.80