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	$236.35	13.441%	$268.1178	$268.12	$268.10	$268.10
Purchase #2	$144.33	13.845%	$164.3125	$164.31	$164.30	$164.30
Purchase #3	$92.47	7.248%	$99.1722	$99.17	$99.15	$99.20
Purchase #4	$168.40	8.246%	$182.2863	$182.29	$182.30	$182.30
Purchase #5	$83.33	8.387%	$90.3189	$90.32	$90.30	$90.30
Purchase #6	$87.44	5.738%	$92.4573	$92.46	$92.45	$92.50
Purchase #7	$76.36	6.373%	$81.2264	$81.23	$81.25	$81.20
7 purchase totals =	$888.68		$977.8914	$977.90	$977.85	$977.90