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	$82.44	11.372%	$91.8151	$91.82	$91.80	$91.80
Purchase #2	$79.32	12.682%	$89.3794	$89.38	$89.40	$89.40
Purchase #3	$56.69	4.262%	$59.1061	$59.11	$59.10	$59.10
Purchase #4	$14.85	5.757%	$15.7049	$15.70	$15.70	$15.70
Purchase #5	$236.59	10.243%	$260.8239	$260.82	$260.80	$260.80
Purchase #6	$228.81	13.589%	$259.903	$259.90	$259.90	$259.90
Purchase #7	$16.43	9.763%	$18.0341	$18.03	$18.05	$18.00
7 purchase totals =	$715.13		$794.7665	$794.76	$794.75	$794.70