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	$137.56	10.618%	$152.1661	$152.17	$152.15	$152.20
Purchase #2	$155.59	9.152%	$169.8296	$169.83	$169.85	$169.80
Purchase #3	$218.30	10.572%	$241.3787	$241.38	$241.40	$241.40
Purchase #4	$135.62	9.426%	$148.4035	$148.40	$148.40	$148.40
Purchase #5	$146.85	3.136%	$151.4552	$151.46	$151.45	$151.50
Purchase #6	$156.70	6.459%	$166.8213	$166.82	$166.80	$166.80
Purchase #7	$135.48	11.538%	$151.1117	$151.11	$151.10	$151.10
7 purchase totals =	$1,086.10		$1,181.1661	$1,181.17	$1,181.15	$1,181.20