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	$111.34	9.837%	$122.2925	$122.29	$122.30	$122.30
Purchase #2	$248.48	6.587%	$264.8474	$264.85	$264.85	$264.80
Purchase #3	$105.73	12.206%	$118.6354	$118.64	$118.65	$118.60
Purchase #4	$139.54	3.142%	$143.9243	$143.92	$143.90	$143.90
Purchase #5	$211.59	12.756%	$238.5804	$238.58	$238.60	$238.60
Purchase #6	$245.90	10.470%	$271.6457	$271.65	$271.65	$271.60
Purchase #7	$66.96	8.324%	$72.5338	$72.53	$72.55	$72.50
7 purchase totals =	$1,129.54		$1,232.4595	$1,232.46	$1,232.50	$1,232.30