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	$134.26	3.656%	$139.1685	$139.17	$139.15	$139.20
Purchase #2	$105.49	3.810%	$109.5092	$109.51	$109.50	$109.50
Purchase #3	$196.40	8.660%	$213.4082	$213.41	$213.40	$213.40
Purchase #4	$155.33	10.424%	$171.5216	$171.52	$171.50	$171.50
Purchase #5	$169.26	12.676%	$190.7154	$190.72	$190.70	$190.70
Purchase #6	$12.90	9.659%	$14.146	$14.15	$14.15	$14.10
Purchase #7	$49.30	13.227%	$55.8209	$55.82	$55.80	$55.80
7 purchase totals =	$822.94		$894.2898	$894.30	$894.20	$894.20