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	$171.63	11.440%	$191.2645	$191.26	$191.25	$191.30
Purchase #2	$168.66	3.410%	$174.4113	$174.41	$174.40	$174.40
Purchase #3	$218.58	3.336%	$225.8718	$225.87	$225.85	$225.90
Purchase #4	$93.44	13.503%	$106.0572	$106.06	$106.05	$106.10
Purchase #5	$123.31	6.694%	$131.5644	$131.56	$131.55	$131.60
Purchase #6	$93.39	6.353%	$99.3231	$99.32	$99.30	$99.30
Purchase #7	$47.31	12.429%	$53.1902	$53.19	$53.20	$53.20
7 purchase totals =	$916.32		$981.6825	$981.67	$981.60	$981.80