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	$150.44	9.710%	$165.0477	$165.05	$165.05	$165.00
Purchase #2	$133.75	6.238%	$142.0933	$142.09	$142.10	$142.10
Purchase #3	$99.33	7.850%	$107.1274	$107.13	$107.15	$107.10
Purchase #4	$110.94	11.412%	$123.6005	$123.60	$123.60	$123.60
Purchase #5	$55.88	12.548%	$62.8918	$62.89	$62.90	$62.90
Purchase #6	$18.53	3.269%	$19.1357	$19.14	$19.15	$19.10
Purchase #7	$170.43	10.661%	$188.5995	$188.60	$188.60	$188.60
7 purchase totals =	$739.30		$808.4959	$808.50	$808.55	$808.40