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	$24.72	13.781%	$28.1267	$28.13	$28.15	$28.10
Purchase #2	$154.33	7.809%	$166.3816	$166.38	$166.40	$166.40
Purchase #3	$79.80	7.568%	$85.8393	$85.84	$85.85	$85.80
Purchase #4	$69.74	9.836%	$76.5996	$76.60	$76.60	$76.60
Purchase #5	$72.87	5.422%	$76.821	$76.82	$76.80	$76.80
Purchase #6	$142.46	6.300%	$151.435	$151.44	$151.45	$151.40
Purchase #7	$32.69	6.709%	$34.8832	$34.88	$34.90	$34.90
7 purchase totals =	$576.61		$620.0864	$620.09	$620.15	$620.00