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	$34.35	11.737%	$38.3817	$38.38	$38.40	$38.40
Purchase #2	$62.30	8.527%	$67.6123	$67.61	$67.60	$67.60
Purchase #3	$245.32	10.608%	$271.3435	$271.34	$271.35	$271.30
Purchase #4	$212.36	3.556%	$219.9115	$219.91	$219.90	$219.90
Purchase #5	$246.70	6.735%	$263.3152	$263.32	$263.30	$263.30
Purchase #6	$191.53	4.748%	$200.6238	$200.62	$200.60	$200.60
Purchase #7	$79.33	6.471%	$84.4634	$84.46	$84.45	$84.50
7 purchase totals =	$1,071.89		$1,145.6514	$1,145.64	$1,145.60	$1,145.60