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	$52.73	5.320%	$55.5352	$55.54	$55.55	$55.50
Purchase #2	$141.64	6.143%	$150.3409	$150.34	$150.35	$150.30
Purchase #3	$45.98	7.792%	$49.5628	$49.56	$49.55	$49.60
Purchase #4	$56.43	9.634%	$61.8665	$61.87	$61.85	$61.90
Purchase #5	$95.85	12.170%	$107.5149	$107.51	$107.50	$107.50
Purchase #6	$99.31	5.222%	$104.496	$104.50	$104.50	$104.50
Purchase #7	$234.35	3.542%	$242.6507	$242.65	$242.65	$242.70
7 purchase totals =	$726.29		$771.9670	$771.97	$771.95	$772.00