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	$133.59	8.864%	$145.4314	$145.43	$145.45	$145.40
Purchase #2	$243.93	8.396%	$264.4104	$264.41	$264.40	$264.40
Purchase #3	$99.60	5.417%	$104.9953	$105.00	$105.00	$105.00
Purchase #4	$59.65	7.517%	$64.1339	$64.13	$64.15	$64.10
Purchase #5	$70.48	8.577%	$76.5251	$76.53	$76.55	$76.50
Purchase #6	$209.88	13.496%	$238.2054	$238.21	$238.20	$238.20
Purchase #7	$84.93	5.302%	$89.433	$89.43	$89.45	$89.40
7 purchase totals =	$902.06		$983.1345	$983.14	$983.20	$983.00