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	$42.30	12.784%	$47.7076	$47.71	$47.70	$47.70
Purchase #2	$40.63	11.704%	$45.3853	$45.39	$45.40	$45.40
Purchase #3	$47.99	12.604%	$54.0387	$54.04	$54.05	$54.00
Purchase #4	$167.74	11.809%	$187.5484	$187.55	$187.55	$187.50
Purchase #5	$97.57	12.118%	$109.3935	$109.39	$109.40	$109.40
Purchase #6	$155.92	8.435%	$169.0719	$169.07	$169.05	$169.10
Purchase #7	$95.36	10.533%	$105.4043	$105.40	$105.40	$105.40
7 purchase totals =	$647.51		$718.5497	$718.55	$718.55	$718.50