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	$27.27	5.297%	$28.7145	$28.71	$28.70	$28.70
Purchase #2	$51.61	11.172%	$57.3759	$57.38	$57.40	$57.40
Purchase #3	$222.78	5.393%	$234.7945	$234.79	$234.80	$234.80
Purchase #4	$182.29	10.164%	$200.818	$200.82	$200.80	$200.80
Purchase #5	$181.74	9.639%	$199.2579	$199.26	$199.25	$199.30
Purchase #6	$157.34	3.477%	$162.8107	$162.81	$162.80	$162.80
Purchase #7	$54.50	4.679%	$57.0501	$57.05	$57.05	$57.10
7 purchase totals =	$877.53		$940.8216	$940.82	$940.80	$940.90