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	$92.93	9.798%	$102.0353	$102.04	$102.05	$102.00
Purchase #2	$65.78	8.128%	$71.1266	$71.13	$71.15	$71.10
Purchase #3	$79.63	4.206%	$82.9792	$82.98	$83.00	$83.00
Purchase #4	$28.72	8.316%	$31.1084	$31.11	$31.10	$31.10
Purchase #5	$31.95	8.443%	$34.6475	$34.65	$34.65	$34.60
Purchase #6	$74.64	5.348%	$78.6317	$78.63	$78.65	$78.60
Purchase #7	$99.73	12.670%	$112.3658	$112.37	$112.35	$112.40
7 purchase totals =	$473.38		$512.8945	$512.91	$512.95	$512.80