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	$149.99	6.568%	$159.8413	$159.84	$159.85	$159.80
Purchase #2	$159.54	6.258%	$169.524	$169.52	$169.50	$169.50
Purchase #3	$19.54	7.350%	$20.9762	$20.98	$21.00	$21.00
Purchase #4	$36.59	3.429%	$37.8447	$37.84	$37.85	$37.80
Purchase #5	$46.25	3.166%	$47.7143	$47.71	$47.70	$47.70
Purchase #6	$72.78	10.684%	$80.5558	$80.56	$80.55	$80.60
Purchase #7	$138.91	3.673%	$144.0122	$144.01	$144.00	$144.00
7 purchase totals =	$623.60		$660.4685	$660.46	$660.45	$660.40