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	$94.61	6.146%	$100.4247	$100.42	$100.40	$100.40
Purchase #2	$94.78	12.399%	$106.5318	$106.53	$106.55	$106.50
Purchase #3	$105.44	13.788%	$119.9781	$119.98	$120.00	$120.00
Purchase #4	$227.97	7.691%	$245.5032	$245.50	$245.50	$245.50
Purchase #5	$241.64	9.277%	$264.0569	$264.06	$264.05	$264.10
Purchase #6	$81.34	8.562%	$88.3043	$88.30	$88.30	$88.30
Purchase #7	$228.90	11.641%	$255.5462	$255.55	$255.55	$255.50
7 purchase totals =	$1,074.68		$1,180.3452	$1,180.34	$1,180.35	$1,180.30