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	$52.50	12.579%	$59.104	$59.10	$59.10	$59.10
Purchase #2	$100.69	9.691%	$110.4479	$110.45	$110.45	$110.40
Purchase #3	$100.58	8.832%	$109.4632	$109.46	$109.45	$109.50
Purchase #4	$85.33	4.809%	$89.4335	$89.43	$89.45	$89.40
Purchase #5	$5.72	9.660%	$6.2726	$6.27	$6.25	$6.30
Purchase #6	$102.34	9.357%	$111.916	$111.92	$111.90	$111.90
Purchase #7	$178.97	10.353%	$197.4988	$197.50	$197.50	$197.50
7 purchase totals =	$626.13		$684.1360	$684.13	$684.10	$684.10