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	$150.88	5.270%	$158.8314	$158.83	$158.85	$158.80
Purchase #2	$90.98	3.630%	$94.2826	$94.28	$94.30	$94.30
Purchase #3	$103.34	6.344%	$109.8959	$109.90	$109.90	$109.90
Purchase #4	$155.61	6.521%	$165.7573	$165.76	$165.75	$165.80
Purchase #5	$26.91	8.230%	$29.1247	$29.12	$29.10	$29.10
Purchase #6	$156.72	6.276%	$166.5557	$166.56	$166.55	$166.60
Purchase #7	$170.28	9.868%	$187.0832	$187.08	$187.10	$187.10
7 purchase totals =	$854.72		$911.5308	$911.53	$911.55	$911.60