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	$53.97	8.437%	$58.5234	$58.52	$58.50	$58.50
Purchase #2	$170.25	13.396%	$193.0567	$193.06	$193.05	$193.10
Purchase #3	$171.63	8.264%	$185.8135	$185.81	$185.80	$185.80
Purchase #4	$129.73	3.710%	$134.543	$134.54	$134.55	$134.50
Purchase #5	$142.76	4.187%	$148.7374	$148.74	$148.75	$148.70
Purchase #6	$104.58	6.866%	$111.7605	$111.76	$111.75	$111.80
Purchase #7	$65.50	10.148%	$72.1469	$72.15	$72.15	$72.10
7 purchase totals =	$838.42		$904.5814	$904.58	$904.55	$904.50