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	$221.75	6.770%	$236.7625	$236.76	$236.75	$236.80
Purchase #2	$109.73	12.690%	$123.6547	$123.65	$123.65	$123.70
Purchase #3	$78.72	4.711%	$82.4285	$82.43	$82.45	$82.40
Purchase #4	$180.95	13.796%	$205.9139	$205.91	$205.90	$205.90
Purchase #5	$175.86	11.463%	$196.0188	$196.02	$196.00	$196.00
Purchase #6	$184.69	4.158%	$192.3694	$192.37	$192.35	$192.40
Purchase #7	$45.98	12.399%	$51.6811	$51.68	$51.70	$51.70
7 purchase totals =	$997.68		$1,088.8289	$1,088.82	$1,088.80	$1,088.90