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	$156.27	3.523%	$161.7754	$161.78	$161.80	$161.80
Purchase #2	$79.48	7.346%	$85.3186	$85.32	$85.30	$85.30
Purchase #3	$103.64	10.874%	$114.9098	$114.91	$114.90	$114.90
Purchase #4	$147.37	13.786%	$167.6864	$167.69	$167.70	$167.70
Purchase #5	$181.32	4.374%	$189.2509	$189.25	$189.25	$189.30
Purchase #6	$172.37	3.185%	$177.86	$177.86	$177.85	$177.90
Purchase #7	$114.92	7.254%	$123.2563	$123.26	$123.25	$123.30
7 purchase totals =	$955.37		$1,020.0574	$1,020.07	$1,020.05	$1,020.20