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	$185.29	11.598%	$206.7799	$206.78	$206.80	$206.80
Purchase #2	$237.61	12.814%	$268.0573	$268.06	$268.05	$268.10
Purchase #3	$71.90	9.662%	$78.847	$78.85	$78.85	$78.80
Purchase #4	$78.76	6.346%	$83.7581	$83.76	$83.75	$83.80
Purchase #5	$111.41	11.153%	$123.8356	$123.84	$123.85	$123.80
Purchase #6	$7.32	3.534%	$7.5787	$7.58	$7.60	$7.60
Purchase #7	$227.44	3.333%	$235.0206	$235.02	$235.00	$235.00
7 purchase totals =	$919.73		$1,003.8772	$1,003.89	$1,003.90	$1,003.90