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	$18.75	10.681%	$20.7527	$20.75	$20.75	$20.80
Purchase #2	$11.33	9.505%	$12.4069	$12.41	$12.40	$12.40
Purchase #3	$199.31	5.207%	$209.6881	$209.69	$209.70	$209.70
Purchase #4	$42.27	6.370%	$44.9626	$44.96	$44.95	$45.00
Purchase #5	$20.91	3.871%	$21.7194	$21.72	$21.70	$21.70
Purchase #6	$149.28	7.732%	$160.8223	$160.82	$160.80	$160.80
Purchase #7	$117.35	11.813%	$131.2126	$131.21	$131.20	$131.20
7 purchase totals =	$559.20		$601.5646	$601.56	$601.50	$601.60