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	$248.92	8.832%	$270.9046	$270.90	$270.90	$270.90
Purchase #2	$124.91	5.301%	$131.5315	$131.53	$131.55	$131.50
Purchase #3	$129.31	4.674%	$135.3539	$135.35	$135.35	$135.40
Purchase #4	$127.36	5.681%	$134.5953	$134.60	$134.60	$134.60
Purchase #5	$147.28	11.755%	$164.5928	$164.59	$164.60	$164.60
Purchase #6	$38.44	13.844%	$43.7616	$43.76	$43.75	$43.80
Purchase #7	$178.95	3.498%	$185.2097	$185.21	$185.20	$185.20
7 purchase totals =	$995.17		$1,065.9494	$1,065.94	$1,065.95	$1,066.00