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	$18.31	10.561%	$20.2437	$20.24	$20.25	$20.20
Purchase #2	$194.98	7.580%	$209.7595	$209.76	$209.75	$209.80
Purchase #3	$153.71	9.774%	$168.7336	$168.73	$168.75	$168.70
Purchase #4	$248.64	10.782%	$275.4484	$275.45	$275.45	$275.40
Purchase #5	$185.82	10.186%	$204.7476	$204.75	$204.75	$204.70
Purchase #6	$52.50	3.485%	$54.3296	$54.33	$54.35	$54.30
Purchase #7	$145.41	11.662%	$162.3677	$162.37	$162.35	$162.40
7 purchase totals =	$999.37		$1,095.6301	$1,095.63	$1,095.65	$1,095.50