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	$39.36	6.521%	$41.9267	$41.93	$41.95	$41.90
Purchase #2	$140.38	12.586%	$158.0482	$158.05	$158.05	$158.00
Purchase #3	$57.27	7.618%	$61.6328	$61.63	$61.65	$61.60
Purchase #4	$232.80	4.479%	$243.2271	$243.23	$243.25	$243.20
Purchase #5	$69.57	4.344%	$72.5921	$72.59	$72.60	$72.60
Purchase #6	$71.55	13.373%	$81.1184	$81.12	$81.10	$81.10
Purchase #7	$211.34	6.269%	$224.5889	$224.59	$224.60	$224.60
7 purchase totals =	$822.27		$883.1342	$883.14	$883.20	$883.00