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	$237.38	5.161%	$249.6312	$249.63	$249.65	$249.60
Purchase #2	$63.47	12.506%	$71.4076	$71.41	$71.40	$71.40
Purchase #3	$173.53	6.819%	$185.363	$185.36	$185.35	$185.40
Purchase #4	$181.28	13.423%	$205.6132	$205.61	$205.60	$205.60
Purchase #5	$75.74	9.376%	$82.8414	$82.84	$82.85	$82.80
Purchase #6	$52.39	13.846%	$59.6439	$59.64	$59.65	$59.60
Purchase #7	$22.61	6.654%	$24.1145	$24.11	$24.10	$24.10
7 purchase totals =	$806.40		$878.6148	$878.60	$878.60	$878.50