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	$68.95	12.299%	$77.4302	$77.43	$77.45	$77.40
Purchase #2	$139.36	9.473%	$152.5616	$152.56	$152.55	$152.60
Purchase #3	$84.33	12.515%	$94.8839	$94.88	$94.90	$94.90
Purchase #4	$210.53	11.847%	$235.4715	$235.47	$235.45	$235.50
Purchase #5	$190.25	5.623%	$200.9478	$200.95	$200.95	$200.90
Purchase #6	$17.75	4.296%	$18.5125	$18.51	$18.50	$18.50
Purchase #7	$128.73	10.698%	$142.5015	$142.50	$142.50	$142.50
7 purchase totals =	$839.90		$922.3090	$922.30	$922.30	$922.30