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	$126.63	6.423%	$134.7634	$134.76	$134.75	$134.80
Purchase #2	$123.54	6.310%	$131.3354	$131.34	$131.35	$131.30
Purchase #3	$157.69	9.819%	$173.1736	$173.17	$173.15	$173.20
Purchase #4	$41.63	4.494%	$43.5009	$43.50	$43.50	$43.50
Purchase #5	$218.39	12.764%	$246.2653	$246.27	$246.25	$246.30
Purchase #6	$227.77	4.254%	$237.4593	$237.46	$237.45	$237.50
Purchase #7	$42.62	7.837%	$45.9601	$45.96	$45.95	$46.00
7 purchase totals =	$938.27		$1,012.4580	$1,012.46	$1,012.40	$1,012.60