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	$75.55	4.375%	$78.8553	$78.86	$78.85	$78.90
Purchase #2	$156.41	7.412%	$168.0031	$168.00	$168.00	$168.00
Purchase #3	$147.26	3.691%	$152.6954	$152.70	$152.70	$152.70
Purchase #4	$20.56	6.275%	$21.8501	$21.85	$21.85	$21.90
Purchase #5	$35.98	12.559%	$40.4987	$40.50	$40.50	$40.50
Purchase #6	$174.42	8.149%	$188.6335	$188.63	$188.65	$188.60
Purchase #7	$163.95	12.166%	$183.8962	$183.90	$183.90	$183.90
7 purchase totals =	$774.13		$834.4323	$834.44	$834.45	$834.50