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	$94.38	4.747%	$98.8602	$98.86	$98.85	$98.90
Purchase #2	$210.39	9.138%	$229.6154	$229.62	$229.60	$229.60
Purchase #3	$143.52	11.202%	$159.5971	$159.60	$159.60	$159.60
Purchase #4	$36.46	8.286%	$39.4811	$39.48	$39.50	$39.50
Purchase #5	$138.27	8.863%	$150.5249	$150.52	$150.50	$150.50
Purchase #6	$101.85	7.524%	$109.5132	$109.51	$109.50	$109.50
Purchase #7	$5.67	10.564%	$6.269	$6.27	$6.25	$6.30
7 purchase totals =	$730.54		$793.8609	$793.86	$793.80	$793.90