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	$140.53	12.863%	$158.6064	$158.61	$158.60	$158.60
Purchase #2	$244.82	10.698%	$271.0108	$271.01	$271.00	$271.00
Purchase #3	$221.56	8.267%	$239.8764	$239.88	$239.90	$239.90
Purchase #4	$167.63	9.692%	$183.8767	$183.88	$183.90	$183.90
Purchase #5	$82.98	8.374%	$89.9287	$89.93	$89.95	$89.90
Purchase #6	$84.35	6.505%	$89.837	$89.84	$89.85	$89.80
Purchase #7	$153.70	7.423%	$165.1092	$165.11	$165.10	$165.10
7 purchase totals =	$1,095.57		$1,198.2452	$1,198.26	$1,198.30	$1,198.20