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	$238.61	4.608%	$249.6051	$249.61	$249.60	$249.60
Purchase #2	$246.45	12.322%	$276.8176	$276.82	$276.80	$276.80
Purchase #3	$211.44	7.175%	$226.6108	$226.61	$226.60	$226.60
Purchase #4	$45.59	3.464%	$47.1692	$47.17	$47.15	$47.20
Purchase #5	$119.51	9.708%	$131.112	$131.11	$131.10	$131.10
Purchase #6	$96.83	3.707%	$100.4195	$100.42	$100.40	$100.40
Purchase #7	$182.30	13.359%	$206.6535	$206.65	$206.65	$206.70
7 purchase totals =	$1,140.73		$1,238.3877	$1,238.39	$1,238.30	$1,238.40