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	$6.78	4.405%	$7.0787	$7.08	$7.10	$7.10
Purchase #2	$45.64	6.142%	$48.4432	$48.44	$48.45	$48.40
Purchase #3	$106.70	4.275%	$111.2614	$111.26	$111.25	$111.30
Purchase #4	$98.98	4.544%	$103.4777	$103.48	$103.50	$103.50
Purchase #5	$148.86	11.760%	$166.3659	$166.37	$166.35	$166.40
Purchase #6	$40.98	13.229%	$46.4012	$46.40	$46.40	$46.40
Purchase #7	$95.33	9.550%	$104.434	$104.43	$104.45	$104.40
7 purchase totals =	$543.27		$587.4621	$587.46	$587.50	$587.50