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	$129.61	5.629%	$136.9057	$136.91	$136.90	$136.90
Purchase #2	$53.49	11.438%	$59.6082	$59.61	$59.60	$59.60
Purchase #3	$219.96	6.834%	$234.9921	$234.99	$235.00	$235.00
Purchase #4	$13.62	7.519%	$14.6441	$14.64	$14.65	$14.60
Purchase #5	$40.52	4.626%	$42.3945	$42.39	$42.40	$42.40
Purchase #6	$86.82	4.330%	$90.5793	$90.58	$90.60	$90.60
Purchase #7	$75.72	6.258%	$80.4586	$80.46	$80.45	$80.50
7 purchase totals =	$619.74		$659.5825	$659.58	$659.60	$659.60