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	$86.61	6.781%	$92.483	$92.48	$92.50	$92.50
Purchase #2	$73.98	8.215%	$80.0575	$80.06	$80.05	$80.10
Purchase #3	$130.94	7.164%	$140.3205	$140.32	$140.30	$140.30
Purchase #4	$153.25	3.864%	$159.1716	$159.17	$159.15	$159.20
Purchase #5	$52.77	12.179%	$59.1969	$59.20	$59.20	$59.20
Purchase #6	$118.40	11.323%	$131.8064	$131.81	$131.80	$131.80
Purchase #7	$131.74	8.522%	$142.9669	$142.97	$142.95	$143.00
7 purchase totals =	$747.69		$806.0028	$806.01	$805.95	$806.10