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	$100.88	7.670%	$108.6175	$108.62	$108.60	$108.60
Purchase #2	$218.85	13.666%	$248.758	$248.76	$248.75	$248.80
Purchase #3	$57.67	13.713%	$65.5783	$65.58	$65.60	$65.60
Purchase #4	$73.63	12.469%	$82.8109	$82.81	$82.80	$82.80
Purchase #5	$130.33	7.464%	$140.0578	$140.06	$140.05	$140.10
Purchase #6	$132.35	4.808%	$138.7134	$138.71	$138.70	$138.70
Purchase #7	$100.61	11.116%	$111.7938	$111.79	$111.80	$111.80
7 purchase totals =	$814.32		$896.3297	$896.33	$896.30	$896.40