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	$7.59	10.849%	$8.4134	$8.41	$8.40	$8.40
Purchase #2	$117.97	8.264%	$127.719	$127.72	$127.70	$127.70
Purchase #3	$133.91	6.272%	$142.3088	$142.31	$142.30	$142.30
Purchase #4	$155.62	9.119%	$169.811	$169.81	$169.80	$169.80
Purchase #5	$158.71	12.769%	$178.9757	$178.98	$179.00	$179.00
Purchase #6	$50.45	11.528%	$56.2659	$56.27	$56.25	$56.30
Purchase #7	$63.83	12.507%	$71.8132	$71.81	$71.80	$71.80
7 purchase totals =	$688.08		$755.3070	$755.31	$755.25	$755.30