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	$45.69	12.687%	$51.4867	$51.49	$51.50	$51.50
Purchase #2	$86.86	9.515%	$95.1247	$95.12	$95.10	$95.10
Purchase #3	$62.92	3.707%	$65.2524	$65.25	$65.25	$65.30
Purchase #4	$198.37	11.486%	$221.1548	$221.15	$221.15	$221.20
Purchase #5	$125.56	11.367%	$139.8324	$139.83	$139.85	$139.80
Purchase #6	$153.65	8.227%	$166.2908	$166.29	$166.30	$166.30
Purchase #7	$185.67	12.844%	$209.5175	$209.52	$209.50	$209.50
7 purchase totals =	$858.72		$948.6593	$948.65	$948.65	$948.70