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	$13.94	6.371%	$14.8281	$14.83	$14.85	$14.80
Purchase #2	$78.74	4.236%	$82.0754	$82.08	$82.10	$82.10
Purchase #3	$73.95	10.151%	$81.4567	$81.46	$81.45	$81.50
Purchase #4	$5.49	3.479%	$5.681	$5.68	$5.70	$5.70
Purchase #5	$58.94	4.287%	$61.4668	$61.47	$61.45	$61.50
Purchase #6	$49.72	9.741%	$54.5632	$54.56	$54.55	$54.60
Purchase #7	$50.86	4.544%	$53.1711	$53.17	$53.15	$53.20
7 purchase totals =	$331.64		$353.2423	$353.25	$353.25	$353.40