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	$54.27	3.478%	$56.1575	$56.16	$56.15	$56.20
Purchase #2	$148.86	13.855%	$169.4846	$169.48	$169.50	$169.50
Purchase #3	$17.80	4.303%	$18.5659	$18.57	$18.55	$18.60
Purchase #4	$120.32	3.108%	$124.0595	$124.06	$124.05	$124.10
Purchase #5	$95.62	4.352%	$99.7814	$99.78	$99.80	$99.80
Purchase #6	$17.33	9.267%	$18.936	$18.94	$18.95	$18.90
Purchase #7	$7.71	7.744%	$8.3071	$8.31	$8.30	$8.30
7 purchase totals =	$461.91		$495.2920	$495.30	$495.30	$495.40