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	$25.46	12.772%	$28.7118	$28.71	$28.70	$28.70
Purchase #2	$209.74	13.728%	$238.5331	$238.53	$238.55	$238.50
Purchase #3	$140.93	8.345%	$152.6906	$152.69	$152.70	$152.70
Purchase #4	$137.51	10.718%	$152.2483	$152.25	$152.25	$152.20
Purchase #5	$162.95	10.513%	$180.0809	$180.08	$180.10	$180.10
Purchase #6	$190.47	7.716%	$205.1667	$205.17	$205.15	$205.20
Purchase #7	$20.35	7.629%	$21.9025	$21.90	$21.90	$21.90
7 purchase totals =	$887.41		$979.3339	$979.33	$979.35	$979.30