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	$199.47	10.499%	$220.4124	$220.41	$220.40	$220.40
Purchase #2	$201.27	13.735%	$228.9144	$228.91	$228.90	$228.90
Purchase #3	$73.36	7.166%	$78.617	$78.62	$78.60	$78.60
Purchase #4	$88.52	9.265%	$96.7214	$96.72	$96.70	$96.70
Purchase #5	$73.56	13.324%	$83.3611	$83.36	$83.35	$83.40
Purchase #6	$127.53	12.713%	$143.7429	$143.74	$143.75	$143.70
Purchase #7	$33.80	13.310%	$38.2988	$38.30	$38.30	$38.30
7 purchase totals =	$797.51		$890.0680	$890.06	$890.00	$890.00