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	$88.42	4.672%	$92.551	$92.55	$92.55	$92.60
Purchase #2	$136.81	5.596%	$144.4659	$144.47	$144.45	$144.50
Purchase #3	$243.27	8.706%	$264.4491	$264.45	$264.45	$264.40
Purchase #4	$72.42	12.641%	$81.5746	$81.57	$81.55	$81.60
Purchase #5	$77.71	9.716%	$85.2603	$85.26	$85.25	$85.30
Purchase #6	$90.99	11.563%	$101.5112	$101.51	$101.50	$101.50
Purchase #7	$43.54	7.108%	$46.6348	$46.63	$46.65	$46.60
7 purchase totals =	$753.16		$816.4469	$816.44	$816.40	$816.50