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	$74.40	5.520%	$78.5069	$78.51	$78.50	$78.50
Purchase #2	$80.85	10.162%	$89.066	$89.07	$89.05	$89.10
Purchase #3	$167.29	12.521%	$188.2364	$188.24	$188.25	$188.20
Purchase #4	$203.52	8.261%	$220.3328	$220.33	$220.35	$220.30
Purchase #5	$35.55	9.478%	$38.9194	$38.92	$38.90	$38.90
Purchase #6	$243.82	6.590%	$259.8877	$259.89	$259.90	$259.90
Purchase #7	$180.78	3.417%	$186.9573	$186.96	$186.95	$187.00
7 purchase totals =	$986.21		$1,061.9065	$1,061.92	$1,061.90	$1,061.90