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	$34.36	5.559%	$36.2701	$36.27	$36.25	$36.30
Purchase #2	$126.88	3.809%	$131.7129	$131.71	$131.70	$131.70
Purchase #3	$18.61	8.559%	$20.2028	$20.20	$20.20	$20.20
Purchase #4	$27.90	9.528%	$30.5583	$30.56	$30.55	$30.60
Purchase #5	$56.44	11.472%	$62.9148	$62.91	$62.90	$62.90
Purchase #6	$118.71	10.619%	$131.3158	$131.32	$131.30	$131.30
Purchase #7	$153.43	13.642%	$174.3609	$174.36	$174.35	$174.40
7 purchase totals =	$536.33		$587.3356	$587.33	$587.25	$587.40