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	$223.40	10.643%	$247.1765	$247.18	$247.20	$247.20
Purchase #2	$63.72	4.830%	$66.7977	$66.80	$66.80	$66.80
Purchase #3	$241.41	3.186%	$249.1013	$249.10	$249.10	$249.10
Purchase #4	$250.96	4.352%	$261.8818	$261.88	$261.90	$261.90
Purchase #5	$241.88	13.230%	$273.8807	$273.88	$273.90	$273.90
Purchase #6	$68.54	3.369%	$70.8491	$70.85	$70.85	$70.80
Purchase #7	$38.98	12.563%	$43.8771	$43.88	$43.90	$43.90
7 purchase totals =	$1,128.89		$1,213.5642	$1,213.57	$1,213.65	$1,213.60