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	$25.50	9.276%	$27.8654	$27.87	$27.85	$27.90
Purchase #2	$98.81	3.411%	$102.1804	$102.18	$102.20	$102.20
Purchase #3	$147.63	5.285%	$155.4322	$155.43	$155.45	$155.40
Purchase #4	$120.68	5.661%	$127.5117	$127.51	$127.50	$127.50
Purchase #5	$79.71	11.825%	$89.1357	$89.14	$89.15	$89.10
Purchase #6	$37.30	8.755%	$40.5656	$40.57	$40.55	$40.60
Purchase #7	$202.59	11.639%	$226.1695	$226.17	$226.15	$226.20
7 purchase totals =	$712.22		$768.8605	$768.87	$768.85	$768.90