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	$238.77	6.518%	$254.333	$254.33	$254.35	$254.30
Purchase #2	$97.47	12.270%	$109.4296	$109.43	$109.45	$109.40
Purchase #3	$99.73	9.113%	$108.8184	$108.82	$108.80	$108.80
Purchase #4	$98.53	8.725%	$107.1267	$107.13	$107.15	$107.10
Purchase #5	$113.63	3.427%	$117.5241	$117.52	$117.50	$117.50
Purchase #6	$48.77	12.329%	$54.7829	$54.78	$54.80	$54.80
Purchase #7	$244.79	9.590%	$268.2654	$268.27	$268.25	$268.30
7 purchase totals =	$941.69		$1,020.2801	$1,020.28	$1,020.30	$1,020.20