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	$170.69	4.554%	$178.4632	$178.46	$178.45	$178.50
Purchase #2	$159.45	9.270%	$174.231	$174.23	$174.25	$174.20
Purchase #3	$180.34	4.585%	$188.6086	$188.61	$188.60	$188.60
Purchase #4	$222.50	10.797%	$246.5233	$246.52	$246.50	$246.50
Purchase #5	$14.30	7.545%	$15.3789	$15.38	$15.40	$15.40
Purchase #6	$225.27	7.160%	$241.3993	$241.40	$241.40	$241.40
Purchase #7	$126.64	12.324%	$142.2471	$142.25	$142.25	$142.20
7 purchase totals =	$1,099.19		$1,186.8514	$1,186.85	$1,186.85	$1,186.80