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	$189.79	10.800%	$210.2873	$210.29	$210.30	$210.30
Purchase #2	$19.72	6.236%	$20.9497	$20.95	$20.95	$20.90
Purchase #3	$34.37	12.478%	$38.6587	$38.66	$38.65	$38.70
Purchase #4	$85.27	5.107%	$89.6247	$89.62	$89.60	$89.60
Purchase #5	$155.35	7.782%	$167.4393	$167.44	$167.45	$167.40
Purchase #6	$245.68	5.633%	$259.5192	$259.52	$259.50	$259.50
Purchase #7	$114.35	4.229%	$119.1859	$119.19	$119.20	$119.20
7 purchase totals =	$844.53		$905.6648	$905.67	$905.65	$905.60