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	$154.34	3.686%	$160.029	$160.03	$160.05	$160.00
Purchase #2	$245.68	5.383%	$258.905	$258.91	$258.90	$258.90
Purchase #3	$151.59	6.496%	$161.4373	$161.44	$161.45	$161.40
Purchase #4	$33.67	11.422%	$37.5158	$37.52	$37.50	$37.50
Purchase #5	$169.33	12.144%	$189.8934	$189.89	$189.90	$189.90
Purchase #6	$31.46	7.752%	$33.8988	$33.90	$33.90	$33.90
Purchase #7	$200.97	7.254%	$215.5484	$215.55	$215.55	$215.50
7 purchase totals =	$987.04		$1,057.2277	$1,057.24	$1,057.25	$1,057.10