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	$232.25	4.213%	$242.0347	$242.03	$242.05	$242.00
Purchase #2	$77.97	6.814%	$83.2829	$83.28	$83.30	$83.30
Purchase #3	$68.94	4.296%	$71.9017	$71.90	$71.90	$71.90
Purchase #4	$115.52	10.294%	$127.4116	$127.41	$127.40	$127.40
Purchase #5	$206.33	6.690%	$220.1335	$220.13	$220.15	$220.10
Purchase #6	$61.86	3.281%	$63.8896	$63.89	$63.90	$63.90
Purchase #7	$242.97	12.466%	$273.2586	$273.26	$273.25	$273.30
7 purchase totals =	$1,005.84		$1,081.9126	$1,081.90	$1,081.95	$1,081.90