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	$12.45	6.338%	$13.2391	$13.24	$13.25	$13.20
Purchase #2	$155.55	7.785%	$167.6596	$167.66	$167.65	$167.70
Purchase #3	$245.61	3.661%	$254.6018	$254.60	$254.60	$254.60
Purchase #4	$30.81	6.718%	$32.8798	$32.88	$32.90	$32.90
Purchase #5	$73.52	8.666%	$79.8912	$79.89	$79.90	$79.90
Purchase #6	$96.63	3.834%	$100.3348	$100.33	$100.35	$100.30
Purchase #7	$219.66	6.726%	$234.4343	$234.43	$234.45	$234.40
7 purchase totals =	$834.23		$883.0406	$883.03	$883.10	$883.00