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	$59.92	5.307%	$63.1	$63.10	$63.10	$63.10
Purchase #2	$165.69	4.296%	$172.808	$172.81	$172.80	$172.80
Purchase #3	$70.90	6.256%	$75.3355	$75.34	$75.35	$75.30
Purchase #4	$112.91	4.428%	$117.9097	$117.91	$117.90	$117.90
Purchase #5	$217.80	3.494%	$225.4099	$225.41	$225.40	$225.40
Purchase #6	$68.89	3.691%	$71.4327	$71.43	$71.45	$71.40
Purchase #7	$99.71	13.650%	$113.3204	$113.32	$113.30	$113.30
7 purchase totals =	$795.82		$839.3162	$839.32	$839.30	$839.20