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	$17.83	13.854%	$20.3002	$20.30	$20.30	$20.30
Purchase #2	$98.43	7.442%	$105.7552	$105.76	$105.75	$105.80
Purchase #3	$243.27	7.817%	$262.2864	$262.29	$262.30	$262.30
Purchase #4	$36.84	6.213%	$39.1289	$39.13	$39.15	$39.10
Purchase #5	$57.78	8.659%	$62.7832	$62.78	$62.80	$62.80
Purchase #6	$102.63	4.731%	$107.4854	$107.49	$107.50	$107.50
Purchase #7	$154.28	5.334%	$162.5093	$162.51	$162.50	$162.50
7 purchase totals =	$711.06		$760.2486	$760.26	$760.30	$760.30