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	$238.33	4.619%	$249.3385	$249.34	$249.35	$249.30
Purchase #2	$96.71	5.173%	$101.7128	$101.71	$101.70	$101.70
Purchase #3	$54.44	8.111%	$58.8556	$58.86	$58.85	$58.90
Purchase #4	$162.96	10.330%	$179.7938	$179.79	$179.80	$179.80
Purchase #5	$236.61	13.116%	$267.6438	$267.64	$267.65	$267.60
Purchase #6	$78.92	12.161%	$88.5175	$88.52	$88.50	$88.50
Purchase #7	$134.28	5.131%	$141.1699	$141.17	$141.15	$141.20
7 purchase totals =	$1,002.25		$1,087.0319	$1,087.03	$1,087.00	$1,087.00