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	$48.89	13.550%	$55.5146	$55.51	$55.50	$55.50
Purchase #2	$151.25	13.184%	$171.1908	$171.19	$171.20	$171.20
Purchase #3	$164.59	9.734%	$180.6112	$180.61	$180.60	$180.60
Purchase #4	$141.32	9.581%	$154.8599	$154.86	$154.85	$154.90
Purchase #5	$190.70	11.322%	$212.2911	$212.29	$212.30	$212.30
Purchase #6	$35.76	3.765%	$37.1064	$37.11	$37.10	$37.10
Purchase #7	$181.56	6.368%	$193.1217	$193.12	$193.10	$193.10
7 purchase totals =	$914.07		$1,004.6957	$1,004.69	$1,004.65	$1,004.70