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	$35.83	10.727%	$39.6735	$39.67	$39.65	$39.70
Purchase #2	$121.66	9.781%	$133.5596	$133.56	$133.55	$133.60
Purchase #3	$210.71	3.661%	$218.4241	$218.42	$218.40	$218.40
Purchase #4	$108.51	6.241%	$115.2821	$115.28	$115.30	$115.30
Purchase #5	$114.75	10.697%	$127.0248	$127.02	$127.00	$127.00
Purchase #6	$243.72	10.302%	$268.828	$268.83	$268.85	$268.80
Purchase #7	$82.61	8.374%	$89.5278	$89.53	$89.55	$89.50
7 purchase totals =	$917.79		$992.3199	$992.31	$992.30	$992.30