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	$116.39	10.497%	$128.6075	$128.61	$128.60	$128.60
Purchase #2	$49.69	9.435%	$54.3783	$54.38	$54.40	$54.40
Purchase #3	$228.33	11.265%	$254.0514	$254.05	$254.05	$254.10
Purchase #4	$48.54	6.837%	$51.8587	$51.86	$51.85	$51.90
Purchase #5	$75.46	3.764%	$78.3003	$78.30	$78.30	$78.30
Purchase #6	$166.34	7.815%	$179.3395	$179.34	$179.35	$179.30
Purchase #7	$238.80	12.685%	$269.0918	$269.09	$269.10	$269.10
7 purchase totals =	$923.55		$1,015.6275	$1,015.63	$1,015.65	$1,015.70