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	$128.83	3.432%	$133.2514	$133.25	$133.25	$133.30
Purchase #2	$121.85	10.290%	$134.3884	$134.39	$134.40	$134.40
Purchase #3	$232.42	4.811%	$243.6017	$243.60	$243.60	$243.60
Purchase #4	$42.43	10.115%	$46.7218	$46.72	$46.70	$46.70
Purchase #5	$100.59	9.265%	$109.9097	$109.91	$109.90	$109.90
Purchase #6	$18.52	12.585%	$20.8507	$20.85	$20.85	$20.90
Purchase #7	$89.56	11.776%	$100.1066	$100.11	$100.10	$100.10
7 purchase totals =	$734.20		$788.8303	$788.83	$788.80	$788.90