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	$130.92	12.855%	$147.7498	$147.75	$147.75	$147.70
Purchase #2	$38.62	9.589%	$42.3233	$42.32	$42.30	$42.30
Purchase #3	$136.68	10.789%	$151.4264	$151.43	$151.45	$151.40
Purchase #4	$219.31	12.323%	$246.3356	$246.34	$246.35	$246.30
Purchase #5	$85.91	12.597%	$96.7321	$96.73	$96.75	$96.70
Purchase #6	$85.45	4.283%	$89.1098	$89.11	$89.10	$89.10
Purchase #7	$27.28	9.348%	$29.8301	$29.83	$29.85	$29.80
7 purchase totals =	$724.17		$803.5071	$803.51	$803.55	$803.30