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	$113.59	9.751%	$124.6662	$124.67	$124.65	$124.70
Purchase #2	$153.82	8.850%	$167.4331	$167.43	$167.45	$167.40
Purchase #3	$141.47	4.494%	$147.8277	$147.83	$147.85	$147.80
Purchase #4	$205.72	6.124%	$218.3183	$218.32	$218.30	$218.30
Purchase #5	$140.51	4.418%	$146.7177	$146.72	$146.70	$146.70
Purchase #6	$38.34	6.470%	$40.8206	$40.82	$40.80	$40.80
Purchase #7	$27.39	5.335%	$28.8513	$28.85	$28.85	$28.90
7 purchase totals =	$820.84		$874.6349	$874.64	$874.60	$874.60