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	$151.86	13.125%	$171.7916	$171.79	$171.80	$171.80
Purchase #2	$250.51	11.862%	$280.2255	$280.23	$280.25	$280.20
Purchase #3	$241.32	8.558%	$261.9722	$261.97	$261.95	$262.00
Purchase #4	$164.36	9.352%	$179.7309	$179.73	$179.75	$179.70
Purchase #5	$218.57	9.290%	$238.8752	$238.88	$238.90	$238.90
Purchase #6	$74.92	7.222%	$80.3307	$80.33	$80.35	$80.30
Purchase #7	$79.31	9.862%	$87.1316	$87.13	$87.15	$87.10
7 purchase totals =	$1,180.85		$1,300.0577	$1,300.06	$1,300.15	$1,300.00