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	$114.60	11.849%	$128.179	$128.18	$128.20	$128.20
Purchase #2	$157.41	11.366%	$175.3012	$175.30	$175.30	$175.30
Purchase #3	$99.90	12.705%	$112.5923	$112.59	$112.60	$112.60
Purchase #4	$19.46	9.751%	$21.3575	$21.36	$21.35	$21.40
Purchase #5	$58.42	5.221%	$61.4701	$61.47	$61.45	$61.50
Purchase #6	$110.43	8.795%	$120.1423	$120.14	$120.15	$120.10
Purchase #7	$37.68	13.196%	$42.6523	$42.65	$42.65	$42.70
7 purchase totals =	$597.90		$661.6947	$661.69	$661.70	$661.80