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	$62.47	7.705%	$67.2833	$67.28	$67.30	$67.30
Purchase #2	$82.82	9.677%	$90.8345	$90.83	$90.85	$90.80
Purchase #3	$150.47	13.558%	$170.8707	$170.87	$170.85	$170.90
Purchase #4	$167.84	12.276%	$188.444	$188.44	$188.45	$188.40
Purchase #5	$175.72	7.678%	$189.2118	$189.21	$189.20	$189.20
Purchase #6	$245.51	4.497%	$256.5506	$256.55	$256.55	$256.60
Purchase #7	$175.53	6.194%	$186.4023	$186.40	$186.40	$186.40
7 purchase totals =	$1,060.36		$1,149.5972	$1,149.58	$1,149.60	$1,149.60