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	$206.51	11.672%	$230.6138	$230.61	$230.60	$230.60
Purchase #2	$55.36	7.819%	$59.6886	$59.69	$59.70	$59.70
Purchase #3	$94.82	8.874%	$103.2343	$103.23	$103.25	$103.20
Purchase #4	$200.63	4.643%	$209.9453	$209.95	$209.95	$209.90
Purchase #5	$181.80	7.474%	$195.3877	$195.39	$195.40	$195.40
Purchase #6	$90.60	9.172%	$98.9098	$98.91	$98.90	$98.90
Purchase #7	$244.80	5.337%	$257.865	$257.87	$257.85	$257.90
7 purchase totals =	$1,074.52		$1,155.6445	$1,155.65	$1,155.65	$1,155.60