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	$11.92	4.326%	$12.4357	$12.44	$12.45	$12.40
Purchase #2	$178.27	8.689%	$193.7599	$193.76	$193.75	$193.80
Purchase #3	$180.56	13.864%	$205.5928	$205.59	$205.60	$205.60
Purchase #4	$83.80	6.690%	$89.4062	$89.41	$89.40	$89.40
Purchase #5	$129.96	9.751%	$142.6324	$142.63	$142.65	$142.60
Purchase #6	$62.66	12.354%	$70.401	$70.40	$70.40	$70.40
Purchase #7	$114.67	7.805%	$123.62	$123.62	$123.60	$123.60
7 purchase totals =	$761.84		$837.8480	$837.85	$837.85	$837.80