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	$164.60	9.418%	$180.102	$180.10	$180.10	$180.10
Purchase #2	$181.97	3.535%	$188.4026	$188.40	$188.40	$188.40
Purchase #3	$71.45	9.777%	$78.4357	$78.44	$78.45	$78.40
Purchase #4	$125.86	9.246%	$137.497	$137.50	$137.50	$137.50
Purchase #5	$84.91	7.520%	$91.2952	$91.30	$91.30	$91.30
Purchase #6	$137.40	11.263%	$152.8754	$152.88	$152.90	$152.90
Purchase #7	$220.65	12.711%	$248.6968	$248.70	$248.70	$248.70
7 purchase totals =	$986.84		$1,077.3047	$1,077.32	$1,077.35	$1,077.30