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	$94.36	6.802%	$100.7784	$100.78	$100.80	$100.80
Purchase #2	$103.36	7.217%	$110.8195	$110.82	$110.80	$110.80
Purchase #3	$48.54	12.564%	$54.6386	$54.64	$54.65	$54.60
Purchase #4	$114.37	7.609%	$123.0724	$123.07	$123.05	$123.10
Purchase #5	$155.89	8.806%	$169.6177	$169.62	$169.60	$169.60
Purchase #6	$90.52	10.343%	$99.8825	$99.88	$99.90	$99.90
Purchase #7	$126.83	5.423%	$133.708	$133.71	$133.70	$133.70
7 purchase totals =	$733.87		$792.5171	$792.52	$792.50	$792.50