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	$102.48	11.790%	$114.5624	$114.56	$114.55	$114.60
Purchase #2	$77.60	10.564%	$85.7977	$85.80	$85.80	$85.80
Purchase #3	$130.55	9.168%	$142.5188	$142.52	$142.50	$142.50
Purchase #4	$125.53	12.229%	$140.8811	$140.88	$140.90	$140.90
Purchase #5	$30.29	10.472%	$33.462	$33.46	$33.45	$33.50
Purchase #6	$110.43	11.691%	$123.3404	$123.34	$123.35	$123.30
Purchase #7	$228.92	9.572%	$250.8322	$250.83	$250.85	$250.80
7 purchase totals =	$805.80		$891.3946	$891.39	$891.40	$891.40