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	$109.35	9.482%	$119.7186	$119.72	$119.70	$119.70
Purchase #2	$213.40	3.777%	$221.4601	$221.46	$221.45	$221.50
Purchase #3	$104.91	4.614%	$109.7505	$109.75	$109.75	$109.80
Purchase #4	$98.86	12.648%	$111.3638	$111.36	$111.35	$111.40
Purchase #5	$5.68	11.146%	$6.3131	$6.31	$6.30	$6.30
Purchase #6	$57.70	5.389%	$60.8095	$60.81	$60.80	$60.80
Purchase #7	$167.35	13.179%	$189.4051	$189.41	$189.40	$189.40
7 purchase totals =	$757.25		$818.8207	$818.82	$818.75	$818.90