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	$53.25	12.484%	$59.8977	$59.90	$59.90	$59.90
Purchase #2	$240.58	10.656%	$266.2162	$266.22	$266.20	$266.20
Purchase #3	$243.32	10.578%	$269.0584	$269.06	$269.05	$269.10
Purchase #4	$142.78	3.680%	$148.0343	$148.03	$148.05	$148.00
Purchase #5	$89.33	11.217%	$99.3501	$99.35	$99.35	$99.40
Purchase #6	$85.30	8.600%	$92.6358	$92.64	$92.65	$92.60
Purchase #7	$244.54	9.676%	$268.2017	$268.20	$268.20	$268.20
7 purchase totals =	$1,099.10		$1,203.3942	$1,203.40	$1,203.40	$1,203.40