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	$43.83	13.211%	$49.6204	$49.62	$49.60	$49.60
Purchase #2	$72.97	9.670%	$80.0262	$80.03	$80.05	$80.00
Purchase #3	$198.87	10.563%	$219.8766	$219.88	$219.90	$219.90
Purchase #4	$55.33	11.345%	$61.6072	$61.61	$61.60	$61.60
Purchase #5	$229.25	5.811%	$242.5717	$242.57	$242.55	$242.60
Purchase #6	$239.72	6.333%	$254.9015	$254.90	$254.90	$254.90
Purchase #7	$93.78	9.191%	$102.3993	$102.40	$102.40	$102.40
7 purchase totals =	$933.75		$1,011.0029	$1,011.01	$1,011.00	$1,011.00