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	$47.91	9.449%	$52.437	$52.44	$52.45	$52.40
Purchase #2	$175.25	8.446%	$190.0516	$190.05	$190.05	$190.10
Purchase #3	$123.58	9.418%	$135.2188	$135.22	$135.20	$135.20
Purchase #4	$224.77	6.280%	$238.8856	$238.89	$238.90	$238.90
Purchase #5	$81.41	9.624%	$89.2449	$89.24	$89.25	$89.20
Purchase #6	$78.27	10.761%	$86.6926	$86.69	$86.70	$86.70
Purchase #7	$203.32	12.525%	$228.7858	$228.79	$228.80	$228.80
7 purchase totals =	$934.51		$1,021.3163	$1,021.32	$1,021.35	$1,021.30