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	$82.36	9.867%	$90.4865	$90.49	$90.50	$90.50
Purchase #2	$74.49	4.543%	$77.8741	$77.87	$77.85	$77.90
Purchase #3	$188.42	5.473%	$198.7322	$198.73	$198.75	$198.70
Purchase #4	$7.59	6.870%	$8.1114	$8.11	$8.10	$8.10
Purchase #5	$152.91	10.562%	$169.0604	$169.06	$169.05	$169.10
Purchase #6	$81.84	9.584%	$89.6835	$89.68	$89.70	$89.70
Purchase #7	$139.67	3.476%	$144.5249	$144.52	$144.50	$144.50
7 purchase totals =	$727.28		$778.4730	$778.46	$778.45	$778.50