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	$103.50	13.825%	$117.8089	$117.81	$117.80	$117.80
Purchase #2	$145.88	13.597%	$165.7153	$165.72	$165.70	$165.70
Purchase #3	$236.88	11.798%	$264.8271	$264.83	$264.85	$264.80
Purchase #4	$243.51	6.722%	$259.8787	$259.88	$259.90	$259.90
Purchase #5	$166.49	9.150%	$181.7238	$181.72	$181.70	$181.70
Purchase #6	$8.27	3.338%	$8.5461	$8.55	$8.55	$8.50
Purchase #7	$97.35	4.607%	$101.8349	$101.83	$101.85	$101.80
7 purchase totals =	$1,001.88		$1,100.3348	$1,100.34	$1,100.35	$1,100.20