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	$95.33	12.787%	$107.5198	$107.52	$107.50	$107.50
Purchase #2	$168.40	8.142%	$182.1111	$182.11	$182.10	$182.10
Purchase #3	$141.27	6.745%	$150.7987	$150.80	$150.80	$150.80
Purchase #4	$76.45	12.273%	$85.8327	$85.83	$85.85	$85.80
Purchase #5	$74.35	7.815%	$80.1605	$80.16	$80.15	$80.20
Purchase #6	$206.64	6.269%	$219.5943	$219.59	$219.60	$219.60
Purchase #7	$48.89	12.733%	$55.1152	$55.12	$55.10	$55.10
7 purchase totals =	$811.33		$881.1323	$881.13	$881.10	$881.10