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	$49.36	3.834%	$51.2525	$51.25	$51.25	$51.30
Purchase #2	$156.98	6.558%	$167.2747	$167.27	$167.25	$167.30
Purchase #3	$44.87	7.690%	$48.3205	$48.32	$48.30	$48.30
Purchase #4	$78.54	10.627%	$86.8864	$86.89	$86.90	$86.90
Purchase #5	$59.68	10.112%	$65.7148	$65.71	$65.70	$65.70
Purchase #6	$37.87	13.164%	$42.8552	$42.86	$42.85	$42.90
Purchase #7	$17.31	7.679%	$18.6392	$18.64	$18.65	$18.60
7 purchase totals =	$444.61		$480.9433	$480.94	$480.90	$481.00