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	$236.39	12.763%	$266.5605	$266.56	$266.55	$266.60
Purchase #2	$89.52	13.657%	$101.7457	$101.75	$101.75	$101.70
Purchase #3	$42.29	13.253%	$47.8947	$47.89	$47.90	$47.90
Purchase #4	$119.55	9.228%	$130.5821	$130.58	$130.60	$130.60
Purchase #5	$97.45	7.730%	$104.9829	$104.98	$105.00	$105.00
Purchase #6	$162.73	5.104%	$171.0357	$171.04	$171.05	$171.00
Purchase #7	$183.59	6.777%	$196.0319	$196.03	$196.05	$196.00
7 purchase totals =	$931.52		$1,018.8335	$1,018.83	$1,018.90	$1,018.80