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	$113.61	13.166%	$128.5679	$128.57	$128.55	$128.60
Purchase #2	$243.77	5.667%	$257.5844	$257.58	$257.60	$257.60
Purchase #3	$30.94	12.801%	$34.9006	$34.90	$34.90	$34.90
Purchase #4	$245.36	9.252%	$268.0607	$268.06	$268.05	$268.10
Purchase #5	$117.96	10.764%	$130.6572	$130.66	$130.65	$130.70
Purchase #6	$112.46	13.226%	$127.334	$127.33	$127.35	$127.30
Purchase #7	$50.80	6.560%	$54.1325	$54.13	$54.15	$54.10
7 purchase totals =	$914.90		$1,001.2373	$1,001.23	$1,001.25	$1,001.30