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	$33.41	13.404%	$37.8883	$37.89	$37.90	$37.90
Purchase #2	$46.40	10.258%	$51.1597	$51.16	$51.15	$51.20
Purchase #3	$104.79	7.849%	$113.015	$113.02	$113.00	$113.00
Purchase #4	$179.69	11.307%	$200.0075	$200.01	$200.00	$200.00
Purchase #5	$10.44	11.272%	$11.6168	$11.62	$11.60	$11.60
Purchase #6	$204.35	4.263%	$213.0614	$213.06	$213.05	$213.10
Purchase #7	$201.25	10.563%	$222.508	$222.51	$222.50	$222.50
7 purchase totals =	$780.33		$849.2567	$849.27	$849.20	$849.30