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	$198.86	13.799%	$226.3007	$226.30	$226.30	$226.30
Purchase #2	$136.88	5.471%	$144.3687	$144.37	$144.35	$144.40
Purchase #3	$47.38	11.743%	$52.9438	$52.94	$52.95	$52.90
Purchase #4	$192.37	13.642%	$218.6131	$218.61	$218.60	$218.60
Purchase #5	$106.26	5.669%	$112.2839	$112.28	$112.30	$112.30
Purchase #6	$57.38	5.321%	$60.4332	$60.43	$60.45	$60.40
Purchase #7	$166.48	13.127%	$188.3338	$188.33	$188.35	$188.30
7 purchase totals =	$905.61		$1,003.2772	$1,003.26	$1,003.30	$1,003.20