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	$47.45	9.805%	$52.1025	$52.10	$52.10	$52.10
Purchase #2	$37.26	10.856%	$41.3049	$41.30	$41.30	$41.30
Purchase #3	$145.37	13.860%	$165.5183	$165.52	$165.50	$165.50
Purchase #4	$119.38	6.501%	$127.1409	$127.14	$127.15	$127.10
Purchase #5	$6.25	8.311%	$6.7694	$6.77	$6.75	$6.80
Purchase #6	$109.87	10.705%	$121.6316	$121.63	$121.65	$121.60
Purchase #7	$59.75	7.731%	$64.3693	$64.37	$64.35	$64.40
7 purchase totals =	$525.33		$578.8369	$578.83	$578.80	$578.80