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	$127.36	13.140%	$144.0951	$144.10	$144.10	$144.10
Purchase #2	$79.58	12.309%	$89.3755	$89.38	$89.40	$89.40
Purchase #3	$178.48	3.590%	$184.8874	$184.89	$184.90	$184.90
Purchase #4	$86.81	5.469%	$91.5576	$91.56	$91.55	$91.60
Purchase #5	$8.48	11.116%	$9.4226	$9.42	$9.40	$9.40
Purchase #6	$123.37	6.471%	$131.3533	$131.35	$131.35	$131.40
Purchase #7	$174.45	3.500%	$180.5558	$180.56	$180.55	$180.60
7 purchase totals =	$778.53		$831.2473	$831.26	$831.25	$831.40