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	$52.55	9.586%	$57.5874	$57.59	$57.60	$57.60
Purchase #2	$72.59	7.447%	$77.9958	$78.00	$78.00	$78.00
Purchase #3	$115.46	13.406%	$130.9386	$130.94	$130.95	$130.90
Purchase #4	$163.77	12.787%	$184.7113	$184.71	$184.70	$184.70
Purchase #5	$200.35	10.863%	$222.114	$222.11	$222.10	$222.10
Purchase #6	$125.81	4.735%	$131.7671	$131.77	$131.75	$131.80
Purchase #7	$83.83	12.159%	$94.0229	$94.02	$94.00	$94.00
7 purchase totals =	$814.36		$899.1371	$899.14	$899.10	$899.10