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	$246.72	13.321%	$279.5856	$279.59	$279.60	$279.60
Purchase #2	$194.91	7.426%	$209.384	$209.38	$209.40	$209.40
Purchase #3	$31.87	10.773%	$35.3034	$35.30	$35.30	$35.30
Purchase #4	$10.37	3.760%	$10.7599	$10.76	$10.75	$10.80
Purchase #5	$145.98	13.514%	$165.7077	$165.71	$165.70	$165.70
Purchase #6	$74.65	8.272%	$80.825	$80.83	$80.85	$80.80
Purchase #7	$84.74	10.439%	$93.586	$93.59	$93.60	$93.60
7 purchase totals =	$789.24		$875.1516	$875.16	$875.20	$875.20