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	$90.73	10.339%	$100.1106	$100.11	$100.10	$100.10
Purchase #2	$183.90	12.501%	$206.8893	$206.89	$206.90	$206.90
Purchase #3	$166.42	12.679%	$187.5204	$187.52	$187.50	$187.50
Purchase #4	$39.33	13.740%	$44.7339	$44.73	$44.75	$44.70
Purchase #5	$19.41	7.753%	$20.9149	$20.91	$20.90	$20.90
Purchase #6	$156.60	7.840%	$168.8774	$168.88	$168.90	$168.90
Purchase #7	$10.31	13.552%	$11.7072	$11.71	$11.70	$11.70
7 purchase totals =	$666.70		$740.7537	$740.75	$740.75	$740.70