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	$165.69	4.339%	$172.8793	$172.88	$172.90	$172.90
Purchase #2	$31.76	4.579%	$33.2143	$33.21	$33.20	$33.20
Purchase #3	$214.43	13.272%	$242.8891	$242.89	$242.90	$242.90
Purchase #4	$158.70	11.261%	$176.5712	$176.57	$176.55	$176.60
Purchase #5	$69.97	4.234%	$72.9325	$72.93	$72.95	$72.90
Purchase #6	$112.91	3.637%	$117.0165	$117.02	$117.00	$117.00
Purchase #7	$19.62	7.170%	$21.0268	$21.03	$21.05	$21.00
7 purchase totals =	$773.08		$836.5297	$836.53	$836.55	$836.50