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	$24.48	13.687%	$27.8306	$27.83	$27.85	$27.80
Purchase #2	$81.89	6.700%	$87.3766	$87.38	$87.40	$87.40
Purchase #3	$75.90	8.810%	$82.5868	$82.59	$82.60	$82.60
Purchase #4	$53.92	11.479%	$60.1095	$60.11	$60.10	$60.10
Purchase #5	$30.69	3.272%	$31.6942	$31.69	$31.70	$31.70
Purchase #6	$191.38	9.522%	$209.6032	$209.60	$209.60	$209.60
Purchase #7	$236.47	10.117%	$260.3937	$260.39	$260.40	$260.40
7 purchase totals =	$694.73		$759.5946	$759.59	$759.65	$759.60