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	$73.66	13.558%	$83.6468	$83.65	$83.65	$83.60
Purchase #2	$54.54	11.348%	$60.7292	$60.73	$60.75	$60.70
Purchase #3	$19.51	8.498%	$21.168	$21.17	$21.15	$21.20
Purchase #4	$145.56	11.657%	$162.5279	$162.53	$162.55	$162.50
Purchase #5	$82.43	9.809%	$90.5156	$90.52	$90.50	$90.50
Purchase #6	$173.96	13.363%	$197.2063	$197.21	$197.20	$197.20
Purchase #7	$48.75	4.740%	$51.0608	$51.06	$51.05	$51.10
7 purchase totals =	$598.41		$666.8546	$666.87	$666.85	$666.80