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	$64.65	7.541%	$69.5253	$69.53	$69.55	$69.50
Purchase #2	$168.43	11.860%	$188.4058	$188.41	$188.40	$188.40
Purchase #3	$33.96	10.676%	$37.5856	$37.59	$37.60	$37.60
Purchase #4	$91.88	13.509%	$104.2921	$104.29	$104.30	$104.30
Purchase #5	$22.49	12.844%	$25.3786	$25.38	$25.40	$25.40
Purchase #6	$91.37	12.562%	$102.8479	$102.85	$102.85	$102.80
Purchase #7	$134.76	3.515%	$139.4968	$139.50	$139.50	$139.50
7 purchase totals =	$607.54		$667.5321	$667.55	$667.60	$667.50