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	$90.93	12.469%	$102.2681	$102.27	$102.25	$102.30
Purchase #2	$48.43	10.718%	$53.6207	$53.62	$53.60	$53.60
Purchase #3	$169.67	11.865%	$189.8013	$189.80	$189.80	$189.80
Purchase #4	$139.32	10.624%	$154.1214	$154.12	$154.10	$154.10
Purchase #5	$244.34	10.640%	$270.3378	$270.34	$270.35	$270.30
Purchase #6	$97.59	6.187%	$103.6279	$103.63	$103.65	$103.60
Purchase #7	$134.51	5.130%	$141.4104	$141.41	$141.40	$141.40
7 purchase totals =	$924.79		$1,015.1876	$1,015.19	$1,015.15	$1,015.10