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	$20.85	4.478%	$21.7837	$21.78	$21.80	$21.80
Purchase #2	$180.46	8.795%	$196.3315	$196.33	$196.35	$196.30
Purchase #3	$221.51	11.527%	$247.0435	$247.04	$247.05	$247.00
Purchase #4	$19.29	9.129%	$21.051	$21.05	$21.05	$21.10
Purchase #5	$89.63	10.326%	$98.8852	$98.89	$98.90	$98.90
Purchase #6	$103.60	11.787%	$115.8113	$115.81	$115.80	$115.80
Purchase #7	$33.81	11.389%	$37.6606	$37.66	$37.65	$37.70
7 purchase totals =	$669.15		$738.5668	$738.56	$738.60	$738.60