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	$112.32	13.604%	$127.6	$127.60	$127.60	$127.60
Purchase #2	$170.85	7.865%	$184.2874	$184.29	$184.30	$184.30
Purchase #3	$218.50	4.354%	$228.0135	$228.01	$228.00	$228.00
Purchase #4	$127.72	12.519%	$143.7093	$143.71	$143.70	$143.70
Purchase #5	$98.78	7.728%	$106.4137	$106.41	$106.40	$106.40
Purchase #6	$201.84	10.639%	$223.3138	$223.31	$223.30	$223.30
Purchase #7	$244.86	9.524%	$268.1805	$268.18	$268.20	$268.20
7 purchase totals =	$1,174.87		$1,281.5182	$1,281.51	$1,281.50	$1,281.50