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	$249.65	9.593%	$273.5989	$273.60	$273.60	$273.60
Purchase #2	$143.26	13.119%	$162.0543	$162.05	$162.05	$162.10
Purchase #3	$39.54	13.595%	$44.9155	$44.92	$44.90	$44.90
Purchase #4	$134.76	6.417%	$143.4075	$143.41	$143.40	$143.40
Purchase #5	$188.56	4.747%	$197.5109	$197.51	$197.50	$197.50
Purchase #6	$55.52	6.304%	$59.02	$59.02	$59.00	$59.00
Purchase #7	$250.91	7.709%	$270.2527	$270.25	$270.25	$270.30
7 purchase totals =	$1,062.20		$1,150.7598	$1,150.76	$1,150.70	$1,150.80