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	$108.27	3.255%	$111.7942	$111.79	$111.80	$111.80
Purchase #2	$86.94	8.189%	$94.0595	$94.06	$94.05	$94.10
Purchase #3	$69.83	12.361%	$78.4617	$78.46	$78.45	$78.50
Purchase #4	$52.38	3.118%	$54.0132	$54.01	$54.00	$54.00
Purchase #5	$243.38	10.443%	$268.7962	$268.80	$268.80	$268.80
Purchase #6	$105.63	7.833%	$113.904	$113.90	$113.90	$113.90
Purchase #7	$55.78	9.425%	$61.0373	$61.04	$61.05	$61.00
7 purchase totals =	$722.21		$782.0661	$782.06	$782.05	$782.10