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	$32.97	13.262%	$37.3425	$37.34	$37.35	$37.30
Purchase #2	$211.69	5.842%	$224.0569	$224.06	$224.05	$224.10
Purchase #3	$114.33	11.453%	$127.4242	$127.42	$127.40	$127.40
Purchase #4	$139.39	4.179%	$145.2151	$145.22	$145.20	$145.20
Purchase #5	$224.68	5.440%	$236.9026	$236.90	$236.90	$236.90
Purchase #6	$102.81	8.275%	$111.3175	$111.32	$111.30	$111.30
Purchase #7	$162.51	4.419%	$169.6913	$169.69	$169.70	$169.70
7 purchase totals =	$988.38		$1,051.9501	$1,051.95	$1,051.90	$1,051.90