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	$59.44	13.144%	$67.2528	$67.25	$67.25	$67.30
Purchase #2	$28.91	5.333%	$30.4518	$30.45	$30.45	$30.50
Purchase #3	$85.27	6.403%	$90.7298	$90.73	$90.75	$90.70
Purchase #4	$177.89	11.612%	$198.5466	$198.55	$198.55	$198.50
Purchase #5	$13.40	5.103%	$14.0838	$14.08	$14.10	$14.10
Purchase #6	$164.32	13.803%	$187.0011	$187.00	$187.00	$187.00
Purchase #7	$238.84	6.681%	$254.7969	$254.80	$254.80	$254.80
7 purchase totals =	$768.07		$842.8628	$842.86	$842.90	$842.90