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	$21.77	12.361%	$24.461	$24.46	$24.45	$24.50
Purchase #2	$211.41	12.821%	$238.5149	$238.51	$238.50	$238.50
Purchase #3	$166.60	5.569%	$175.878	$175.88	$175.90	$175.90
Purchase #4	$11.33	3.631%	$11.7414	$11.74	$11.75	$11.70
Purchase #5	$79.69	13.483%	$90.4346	$90.43	$90.45	$90.40
Purchase #6	$163.28	13.349%	$185.0762	$185.08	$185.10	$185.10
Purchase #7	$110.71	12.308%	$124.3362	$124.34	$124.35	$124.30
7 purchase totals =	$764.79		$850.4423	$850.44	$850.50	$850.40