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	$125.36	13.645%	$142.4654	$142.47	$142.45	$142.50
Purchase #2	$191.55	3.849%	$198.9228	$198.92	$198.90	$198.90
Purchase #3	$138.42	10.798%	$153.3666	$153.37	$153.35	$153.40
Purchase #4	$135.83	7.120%	$145.5011	$145.50	$145.50	$145.50
Purchase #5	$78.96	3.259%	$81.5333	$81.53	$81.55	$81.50
Purchase #6	$49.31	13.782%	$56.1059	$56.11	$56.10	$56.10
Purchase #7	$82.37	8.708%	$89.5428	$89.54	$89.55	$89.50
7 purchase totals =	$801.80		$867.4379	$867.44	$867.40	$867.40