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	$174.49	4.238%	$181.8849	$181.88	$181.90	$181.90
Purchase #2	$72.96	9.505%	$79.8948	$79.89	$79.90	$79.90
Purchase #3	$96.38	13.598%	$109.4858	$109.49	$109.50	$109.50
Purchase #4	$99.40	12.739%	$112.0626	$112.06	$112.05	$112.10
Purchase #5	$145.87	4.604%	$152.5859	$152.59	$152.60	$152.60
Purchase #6	$163.36	9.109%	$178.2405	$178.24	$178.25	$178.20
Purchase #7	$87.64	13.426%	$99.4065	$99.41	$99.40	$99.40
7 purchase totals =	$840.10		$913.5610	$913.56	$913.60	$913.60