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	$172.66	3.187%	$178.1627	$178.16	$178.15	$178.20
Purchase #2	$73.75	10.551%	$81.5314	$81.53	$81.55	$81.50
Purchase #3	$82.72	9.433%	$90.523	$90.52	$90.50	$90.50
Purchase #4	$29.62	9.289%	$32.3714	$32.37	$32.35	$32.40
Purchase #5	$247.51	9.106%	$270.0483	$270.05	$270.05	$270.00
Purchase #6	$173.92	4.785%	$182.2421	$182.24	$182.25	$182.20
Purchase #7	$83.26	7.577%	$89.5686	$89.57	$89.55	$89.60
7 purchase totals =	$863.44		$924.4475	$924.44	$924.40	$924.40