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	$149.34	10.381%	$164.843	$164.84	$164.85	$164.80
Purchase #2	$208.73	9.309%	$228.1607	$228.16	$228.15	$228.20
Purchase #3	$139.47	11.464%	$155.4588	$155.46	$155.45	$155.50
Purchase #4	$54.98	11.837%	$61.488	$61.49	$61.50	$61.50
Purchase #5	$223.94	6.320%	$238.093	$238.09	$238.10	$238.10
Purchase #6	$51.73	13.292%	$58.606	$58.61	$58.60	$58.60
Purchase #7	$42.39	3.408%	$43.8347	$43.83	$43.85	$43.80
7 purchase totals =	$870.58		$950.4842	$950.48	$950.50	$950.50