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	$38.41	10.535%	$42.4565	$42.46	$42.45	$42.50
Purchase #2	$229.31	11.646%	$256.0154	$256.02	$256.00	$256.00
Purchase #3	$136.79	8.756%	$148.7673	$148.77	$148.75	$148.80
Purchase #4	$190.89	9.872%	$209.7347	$209.73	$209.75	$209.70
Purchase #5	$126.67	11.703%	$141.4942	$141.49	$141.50	$141.50
Purchase #6	$20.32	11.428%	$22.6422	$22.64	$22.65	$22.60
Purchase #7	$99.36	3.420%	$102.7581	$102.76	$102.75	$102.80
7 purchase totals =	$841.75		$923.8684	$923.87	$923.85	$923.90