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	$140.59	3.337%	$145.2815	$145.28	$145.30	$145.30
Purchase #2	$32.28	13.655%	$36.6878	$36.69	$36.70	$36.70
Purchase #3	$249.81	7.632%	$268.8755	$268.88	$268.90	$268.90
Purchase #4	$242.62	6.301%	$257.9075	$257.91	$257.90	$257.90
Purchase #5	$43.72	4.833%	$45.833	$45.83	$45.85	$45.80
Purchase #6	$81.47	11.320%	$90.6924	$90.69	$90.70	$90.70
Purchase #7	$235.51	4.522%	$246.1598	$246.16	$246.15	$246.20
7 purchase totals =	$1,026.00		$1,091.4375	$1,091.44	$1,091.50	$1,091.50