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	$69.54	12.637%	$78.3278	$78.33	$78.35	$78.30
Purchase #2	$29.30	8.625%	$31.8271	$31.83	$31.85	$31.80
Purchase #3	$107.27	12.373%	$120.5425	$120.54	$120.55	$120.50
Purchase #4	$238.38	13.354%	$270.2133	$270.21	$270.20	$270.20
Purchase #5	$136.93	7.339%	$146.9793	$146.98	$147.00	$147.00
Purchase #6	$39.94	13.853%	$45.4729	$45.47	$45.45	$45.50
Purchase #7	$179.99	4.870%	$188.7555	$188.76	$188.75	$188.80
7 purchase totals =	$801.35		$882.1184	$882.12	$882.15	$882.10