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	$45.51	5.233%	$47.8915	$47.89	$47.90	$47.90
Purchase #2	$125.74	8.183%	$136.0293	$136.03	$136.05	$136.00
Purchase #3	$200.71	11.475%	$223.7415	$223.74	$223.75	$223.70
Purchase #4	$164.40	9.675%	$180.3057	$180.31	$180.30	$180.30
Purchase #5	$238.98	10.625%	$264.3716	$264.37	$264.35	$264.40
Purchase #6	$127.89	12.778%	$144.2318	$144.23	$144.25	$144.20
Purchase #7	$250.32	5.682%	$264.5432	$264.54	$264.55	$264.50
7 purchase totals =	$1,153.55		$1,261.1146	$1,261.11	$1,261.15	$1,261.00