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	$100.74	3.739%	$104.5067	$104.51	$104.50	$104.50
Purchase #2	$70.96	13.636%	$80.6361	$80.64	$80.65	$80.60
Purchase #3	$168.62	13.356%	$191.1409	$191.14	$191.15	$191.10
Purchase #4	$36.75	11.191%	$40.8627	$40.86	$40.85	$40.90
Purchase #5	$127.35	3.570%	$131.8964	$131.90	$131.90	$131.90
Purchase #6	$164.37	13.215%	$186.0915	$186.09	$186.10	$186.10
Purchase #7	$150.61	12.172%	$168.9422	$168.94	$168.95	$168.90
7 purchase totals =	$819.40		$904.0765	$904.08	$904.10	$904.00