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	$133.91	4.421%	$139.8302	$139.83	$139.85	$139.80
Purchase #2	$90.50	6.657%	$96.5246	$96.52	$96.50	$96.50
Purchase #3	$6.56	11.275%	$7.2996	$7.30	$7.30	$7.30
Purchase #4	$116.51	5.606%	$123.0416	$123.04	$123.05	$123.00
Purchase #5	$49.38	13.521%	$56.0567	$56.06	$56.05	$56.10
Purchase #6	$101.38	11.442%	$112.9799	$112.98	$113.00	$113.00
Purchase #7	$208.58	4.223%	$217.3883	$217.39	$217.40	$217.40
7 purchase totals =	$706.82		$753.1209	$753.12	$753.15	$753.10