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	$181.79	4.550%	$190.0614	$190.06	$190.05	$190.10
Purchase #2	$128.51	8.258%	$139.1224	$139.12	$139.10	$139.10
Purchase #3	$5.53	7.624%	$5.9516	$5.95	$5.95	$6.00
Purchase #4	$18.57	13.297%	$21.0393	$21.04	$21.05	$21.00
Purchase #5	$250.94	11.872%	$280.7316	$280.73	$280.75	$280.70
Purchase #6	$13.88	3.830%	$14.4116	$14.41	$14.40	$14.40
Purchase #7	$13.55	10.200%	$14.9321	$14.93	$14.95	$14.90
7 purchase totals =	$612.77		$666.2500	$666.24	$666.25	$666.20