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	$25.75	10.552%	$28.4671	$28.47	$28.45	$28.50
Purchase #2	$143.78	4.336%	$150.0143	$150.01	$150.00	$150.00
Purchase #3	$33.82	11.579%	$37.736	$37.74	$37.75	$37.70
Purchase #4	$137.42	3.609%	$142.3795	$142.38	$142.40	$142.40
Purchase #5	$193.53	3.580%	$200.4584	$200.46	$200.45	$200.50
Purchase #6	$155.31	6.741%	$165.7794	$165.78	$165.80	$165.80
Purchase #7	$25.53	6.604%	$27.216	$27.22	$27.20	$27.20
7 purchase totals =	$715.14		$752.0507	$752.06	$752.05	$752.10