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	$53.36	3.638%	$55.3012	$55.30	$55.30	$55.30
Purchase #2	$72.53	9.689%	$79.5574	$79.56	$79.55	$79.60
Purchase #3	$37.68	12.547%	$42.4077	$42.41	$42.40	$42.40
Purchase #4	$46.85	11.534%	$52.2537	$52.25	$52.25	$52.30
Purchase #5	$210.76	3.715%	$218.5897	$218.59	$218.60	$218.60
Purchase #6	$164.69	8.629%	$178.9011	$178.90	$178.90	$178.90
Purchase #7	$188.96	7.631%	$203.3795	$203.38	$203.40	$203.40
7 purchase totals =	$774.83		$830.3903	$830.39	$830.40	$830.50