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	$188.91	8.292%	$204.5744	$204.57	$204.55	$204.60
Purchase #2	$139.50	12.843%	$157.416	$157.42	$157.40	$157.40
Purchase #3	$187.87	4.651%	$196.6078	$196.61	$196.60	$196.60
Purchase #4	$140.33	13.120%	$158.7413	$158.74	$158.75	$158.70
Purchase #5	$242.85	10.481%	$268.3031	$268.30	$268.30	$268.30
Purchase #6	$242.71	10.395%	$267.9397	$267.94	$267.95	$267.90
Purchase #7	$54.52	9.300%	$59.5904	$59.59	$59.60	$59.60
7 purchase totals =	$1,196.69		$1,313.1727	$1,313.17	$1,313.15	$1,313.10