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	$242.63	10.662%	$268.4992	$268.50	$268.50	$268.50
Purchase #2	$223.85	7.874%	$241.4759	$241.48	$241.50	$241.50
Purchase #3	$83.32	4.113%	$86.747	$86.75	$86.75	$86.70
Purchase #4	$65.44	10.425%	$72.2621	$72.26	$72.25	$72.30
Purchase #5	$166.99	5.421%	$176.0425	$176.04	$176.05	$176.00
Purchase #6	$104.59	4.566%	$109.3656	$109.37	$109.35	$109.40
Purchase #7	$61.65	6.779%	$65.8293	$65.83	$65.85	$65.80
7 purchase totals =	$948.47		$1,020.2216	$1,020.23	$1,020.25	$1,020.20