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	$100.84	3.659%	$104.5297	$104.53	$104.55	$104.50
Purchase #2	$102.47	9.871%	$112.5848	$112.58	$112.60	$112.60
Purchase #3	$216.33	9.166%	$236.1588	$236.16	$236.15	$236.20
Purchase #4	$246.86	13.481%	$280.1392	$280.14	$280.15	$280.10
Purchase #5	$89.41	3.511%	$92.5492	$92.55	$92.55	$92.50
Purchase #6	$153.70	3.170%	$158.5723	$158.57	$158.55	$158.60
Purchase #7	$156.75	10.190%	$172.7228	$172.72	$172.70	$172.70
7 purchase totals =	$1,066.36		$1,157.2568	$1,157.25	$1,157.25	$1,157.20