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	$98.37	4.733%	$103.0259	$103.03	$103.05	$103.00
Purchase #2	$68.69	6.457%	$73.1253	$73.13	$73.15	$73.10
Purchase #3	$164.76	13.454%	$186.9268	$186.93	$186.95	$186.90
Purchase #4	$61.53	9.338%	$67.2757	$67.28	$67.30	$67.30
Purchase #5	$115.71	10.514%	$127.8757	$127.88	$127.90	$127.90
Purchase #6	$92.37	10.486%	$102.0559	$102.06	$102.05	$102.10
Purchase #7	$222.56	12.293%	$249.9193	$249.92	$249.90	$249.90
7 purchase totals =	$823.99		$910.2046	$910.23	$910.30	$910.20