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	$235.46	12.727%	$265.427	$265.43	$265.45	$265.40
Purchase #2	$173.71	5.385%	$183.0643	$183.06	$183.05	$183.10
Purchase #3	$215.49	12.716%	$242.8917	$242.89	$242.90	$242.90
Purchase #4	$79.31	7.274%	$85.079	$85.08	$85.10	$85.10
Purchase #5	$37.57	12.814%	$42.3842	$42.38	$42.40	$42.40
Purchase #6	$195.97	8.410%	$212.4511	$212.45	$212.45	$212.50
Purchase #7	$244.98	4.242%	$255.3721	$255.37	$255.35	$255.40
7 purchase totals =	$1,182.49		$1,286.6694	$1,286.66	$1,286.70	$1,286.80