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	$77.72	4.726%	$81.393	$81.39	$81.40	$81.40
Purchase #2	$43.91	8.402%	$47.5993	$47.60	$47.60	$47.60
Purchase #3	$85.56	4.811%	$89.6763	$89.68	$89.70	$89.70
Purchase #4	$140.54	5.847%	$148.7574	$148.76	$148.75	$148.80
Purchase #5	$118.55	10.690%	$131.223	$131.22	$131.20	$131.20
Purchase #6	$116.73	9.384%	$127.6839	$127.68	$127.70	$127.70
Purchase #7	$210.37	11.556%	$234.6804	$234.68	$234.70	$234.70
7 purchase totals =	$793.38		$861.0133	$861.01	$861.05	$861.10