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	$139.54	5.473%	$147.177	$147.18	$147.20	$147.20
Purchase #2	$169.51	9.407%	$185.4558	$185.46	$185.45	$185.50
Purchase #3	$63.72	12.626%	$71.7653	$71.77	$71.75	$71.80
Purchase #4	$37.45	6.810%	$40.0003	$40.00	$40.00	$40.00
Purchase #5	$36.52	8.349%	$39.5691	$39.57	$39.55	$39.60
Purchase #6	$41.42	12.610%	$46.6431	$46.64	$46.65	$46.60
Purchase #7	$197.78	6.114%	$209.8723	$209.87	$209.85	$209.90
7 purchase totals =	$685.94		$740.4829	$740.49	$740.45	$740.60