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	$44.58	7.421%	$47.8883	$47.89	$47.90	$47.90
Purchase #2	$113.83	8.549%	$123.5613	$123.56	$123.55	$123.60
Purchase #3	$109.49	5.317%	$115.3116	$115.31	$115.30	$115.30
Purchase #4	$208.82	10.803%	$231.3788	$231.38	$231.40	$231.40
Purchase #5	$60.65	11.456%	$67.5981	$67.60	$67.60	$67.60
Purchase #6	$155.85	11.498%	$173.7696	$173.77	$173.75	$173.80
Purchase #7	$77.91	10.741%	$86.2783	$86.28	$86.30	$86.30
7 purchase totals =	$771.13		$845.7860	$845.79	$845.80	$845.90