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	$26.40	9.692%	$28.9587	$28.96	$28.95	$29.00
Purchase #2	$148.47	5.374%	$156.4488	$156.45	$156.45	$156.40
Purchase #3	$155.70	4.566%	$162.8093	$162.81	$162.80	$162.80
Purchase #4	$99.82	11.606%	$111.4051	$111.41	$111.40	$111.40
Purchase #5	$148.29	11.779%	$165.7571	$165.76	$165.75	$165.80
Purchase #6	$5.25	12.642%	$5.9137	$5.91	$5.90	$5.90
Purchase #7	$182.57	12.199%	$204.8417	$204.84	$204.85	$204.80
7 purchase totals =	$766.50		$836.1344	$836.14	$836.10	$836.10