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	$161.93	4.426%	$169.097	$169.10	$169.10	$169.10
Purchase #2	$125.59	8.409%	$136.1509	$136.15	$136.15	$136.20
Purchase #3	$130.59	12.386%	$146.7649	$146.76	$146.75	$146.80
Purchase #4	$19.93	7.322%	$21.3893	$21.39	$21.40	$21.40
Purchase #5	$165.44	6.669%	$176.4732	$176.47	$176.45	$176.50
Purchase #6	$231.45	13.218%	$262.0431	$262.04	$262.05	$262.00
Purchase #7	$80.94	11.259%	$90.053	$90.05	$90.05	$90.10
7 purchase totals =	$915.87		$1,001.9714	$1,001.96	$1,001.95	$1,002.10