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	$178.68	11.485%	$199.2014	$199.20	$199.20	$199.20
Purchase #2	$37.62	7.752%	$40.5363	$40.54	$40.55	$40.50
Purchase #3	$102.72	3.591%	$106.4087	$106.41	$106.40	$106.40
Purchase #4	$141.84	10.589%	$156.8594	$156.86	$156.85	$156.90
Purchase #5	$41.34	13.450%	$46.9002	$46.90	$46.90	$46.90
Purchase #6	$44.82	9.713%	$49.1734	$49.17	$49.15	$49.20
Purchase #7	$56.33	5.819%	$59.6078	$59.61	$59.60	$59.60
7 purchase totals =	$603.35		$658.6872	$658.69	$658.65	$658.70