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	$130.59	9.828%	$143.4244	$143.42	$143.40	$143.40
Purchase #2	$101.94	6.276%	$108.3378	$108.34	$108.35	$108.30
Purchase #3	$186.52	7.416%	$200.3523	$200.35	$200.35	$200.40
Purchase #4	$131.38	11.539%	$146.5399	$146.54	$146.55	$146.50
Purchase #5	$30.56	9.159%	$33.359	$33.36	$33.35	$33.40
Purchase #6	$84.62	6.159%	$89.8317	$89.83	$89.85	$89.80
Purchase #7	$170.95	4.760%	$179.0872	$179.09	$179.10	$179.10
7 purchase totals =	$836.56		$900.9323	$900.93	$900.95	$900.90