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	$162.39	11.608%	$181.2402	$181.24	$181.25	$181.20
Purchase #2	$56.80	4.847%	$59.5531	$59.55	$59.55	$59.60
Purchase #3	$107.37	7.319%	$115.2284	$115.23	$115.25	$115.20
Purchase #4	$77.38	6.293%	$82.2495	$82.25	$82.25	$82.20
Purchase #5	$118.50	3.158%	$122.2422	$122.24	$122.25	$122.20
Purchase #6	$111.42	11.179%	$123.8756	$123.88	$123.90	$123.90
Purchase #7	$217.93	7.398%	$234.0525	$234.05	$234.05	$234.10
7 purchase totals =	$851.79		$918.4415	$918.44	$918.50	$918.40