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	$114.32	5.522%	$120.6328	$120.63	$120.65	$120.60
Purchase #2	$54.33	9.384%	$59.4283	$59.43	$59.45	$59.40
Purchase #3	$204.71	3.635%	$212.1512	$212.15	$212.15	$212.20
Purchase #4	$19.53	5.353%	$20.5754	$20.58	$20.60	$20.60
Purchase #5	$189.81	10.592%	$209.9147	$209.91	$209.90	$209.90
Purchase #6	$76.38	12.455%	$85.8931	$85.89	$85.90	$85.90
Purchase #7	$84.87	5.791%	$89.7848	$89.78	$89.80	$89.80
7 purchase totals =	$743.95		$798.3803	$798.37	$798.45	$798.40