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	$53.95	6.342%	$57.3715	$57.37	$57.35	$57.40
Purchase #2	$19.31	11.547%	$21.5397	$21.54	$21.55	$21.50
Purchase #3	$86.71	3.829%	$90.0301	$90.03	$90.05	$90.00
Purchase #4	$238.28	4.765%	$249.634	$249.63	$249.65	$249.60
Purchase #5	$169.57	11.380%	$188.8671	$188.87	$188.85	$188.90
Purchase #6	$31.59	5.588%	$33.3552	$33.36	$33.35	$33.40
Purchase #7	$246.73	7.158%	$264.3909	$264.39	$264.40	$264.40
7 purchase totals =	$846.14		$905.1885	$905.19	$905.20	$905.20