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	$169.61	10.739%	$187.8244	$187.82	$187.80	$187.80
Purchase #2	$49.69	7.534%	$53.4336	$53.43	$53.45	$53.40
Purchase #3	$85.90	4.821%	$90.0412	$90.04	$90.05	$90.00
Purchase #4	$64.92	11.535%	$72.4085	$72.41	$72.40	$72.40
Purchase #5	$124.46	5.600%	$131.4298	$131.43	$131.45	$131.40
Purchase #6	$134.28	5.134%	$141.1739	$141.17	$141.15	$141.20
Purchase #7	$174.80	8.734%	$190.067	$190.07	$190.05	$190.10
7 purchase totals =	$803.66		$866.3784	$866.37	$866.35	$866.30