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	$76.46	9.827%	$83.9737	$83.97	$83.95	$84.00
Purchase #2	$81.59	10.159%	$89.8787	$89.88	$89.90	$89.90
Purchase #3	$90.42	12.622%	$101.8328	$101.83	$101.85	$101.80
Purchase #4	$79.86	7.261%	$85.6586	$85.66	$85.65	$85.70
Purchase #5	$130.65	13.654%	$148.489	$148.49	$148.50	$148.50
Purchase #6	$167.53	13.836%	$190.7095	$190.71	$190.70	$190.70
Purchase #7	$73.62	8.380%	$79.7894	$79.79	$79.80	$79.80
7 purchase totals =	$700.13		$780.3317	$780.33	$780.35	$780.40