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	$55.39	6.788%	$59.1499	$59.15	$59.15	$59.10
Purchase #2	$155.40	6.261%	$165.1296	$165.13	$165.15	$165.10
Purchase #3	$52.54	12.524%	$59.1201	$59.12	$59.10	$59.10
Purchase #4	$140.52	10.835%	$155.7453	$155.75	$155.75	$155.70
Purchase #5	$26.97	12.680%	$30.3898	$30.39	$30.40	$30.40
Purchase #6	$27.80	5.224%	$29.2523	$29.25	$29.25	$29.30
Purchase #7	$217.45	5.475%	$229.3554	$229.36	$229.35	$229.40
7 purchase totals =	$676.07		$728.1424	$728.15	$728.15	$728.10