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	$236.86	6.126%	$251.37	$251.37	$251.35	$251.40
Purchase #2	$171.81	11.356%	$191.3207	$191.32	$191.30	$191.30
Purchase #3	$225.49	6.857%	$240.9518	$240.95	$240.95	$241.00
Purchase #4	$31.73	5.740%	$33.5513	$33.55	$33.55	$33.60
Purchase #5	$17.70	3.432%	$18.3075	$18.31	$18.30	$18.30
Purchase #6	$245.42	10.140%	$270.3056	$270.31	$270.30	$270.30
Purchase #7	$62.55	7.807%	$67.4333	$67.43	$67.45	$67.40
7 purchase totals =	$991.56		$1,073.2402	$1,073.24	$1,073.20	$1,073.30