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	$85.80	8.508%	$93.0999	$93.10	$93.10	$93.10
Purchase #2	$36.61	3.211%	$37.7855	$37.79	$37.80	$37.80
Purchase #3	$80.32	6.723%	$85.7199	$85.72	$85.70	$85.70
Purchase #4	$242.53	9.412%	$265.3569	$265.36	$265.35	$265.40
Purchase #5	$234.60	13.213%	$265.5977	$265.60	$265.60	$265.60
Purchase #6	$165.85	3.366%	$171.4325	$171.43	$171.45	$171.40
Purchase #7	$159.70	6.744%	$170.4702	$170.47	$170.45	$170.50
7 purchase totals =	$1,005.41		$1,089.4626	$1,089.47	$1,089.45	$1,089.50