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	$171.86	3.576%	$178.0057	$178.01	$178.00	$178.00
Purchase #2	$88.37	13.316%	$100.1373	$100.14	$100.15	$100.10
Purchase #3	$237.56	12.803%	$267.9748	$267.97	$267.95	$268.00
Purchase #4	$62.64	13.250%	$70.9398	$70.94	$70.95	$70.90
Purchase #5	$49.45	5.219%	$52.0308	$52.03	$52.05	$52.00
Purchase #6	$89.52	11.365%	$99.6939	$99.69	$99.70	$99.70
Purchase #7	$197.97	3.606%	$205.1088	$205.11	$205.10	$205.10
7 purchase totals =	$897.37		$973.8911	$973.89	$973.90	$973.80