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	$98.60	10.266%	$108.7223	$108.72	$108.70	$108.70
Purchase #2	$87.42	3.214%	$90.2297	$90.23	$90.25	$90.20
Purchase #3	$5.98	9.335%	$6.5382	$6.54	$6.55	$6.50
Purchase #4	$10.44	8.825%	$11.3613	$11.36	$11.35	$11.40
Purchase #5	$67.81	6.430%	$72.1702	$72.17	$72.15	$72.20
Purchase #6	$31.76	4.615%	$33.2257	$33.23	$33.25	$33.20
Purchase #7	$117.43	9.346%	$128.405	$128.41	$128.40	$128.40
7 purchase totals =	$419.44		$450.6524	$450.66	$450.65	$450.60