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	$150.41	12.588%	$169.3436	$169.34	$169.35	$169.30
Purchase #2	$100.74	8.656%	$109.4601	$109.46	$109.45	$109.50
Purchase #3	$132.47	5.278%	$139.4618	$139.46	$139.45	$139.50
Purchase #4	$67.75	12.755%	$76.3915	$76.39	$76.40	$76.40
Purchase #5	$184.52	11.701%	$206.1107	$206.11	$206.10	$206.10
Purchase #6	$79.87	12.445%	$89.8098	$89.81	$89.80	$89.80
Purchase #7	$150.94	5.533%	$159.2915	$159.29	$159.30	$159.30
7 purchase totals =	$866.70		$949.8690	$949.86	$949.85	$949.90