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	$60.92	6.490%	$64.8737	$64.87	$64.85	$64.90
Purchase #2	$177.61	10.538%	$196.3265	$196.33	$196.35	$196.30
Purchase #3	$156.92	9.422%	$171.705	$171.71	$171.70	$171.70
Purchase #4	$84.71	5.551%	$89.4123	$89.41	$89.40	$89.40
Purchase #5	$23.71	12.315%	$26.6299	$26.63	$26.65	$26.60
Purchase #6	$233.66	13.603%	$265.4448	$265.44	$265.45	$265.40
Purchase #7	$161.33	3.687%	$167.2782	$167.28	$167.30	$167.30
7 purchase totals =	$898.86		$981.6704	$981.67	$981.70	$981.60