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	$50.82	4.769%	$53.2436	$53.24	$53.25	$53.20
Purchase #2	$182.48	6.740%	$194.7792	$194.78	$194.80	$194.80
Purchase #3	$78.57	12.231%	$88.1799	$88.18	$88.20	$88.20
Purchase #4	$20.33	12.566%	$22.8847	$22.88	$22.90	$22.90
Purchase #5	$177.39	10.517%	$196.0461	$196.05	$196.05	$196.00
Purchase #6	$57.59	11.679%	$64.3159	$64.32	$64.30	$64.30
Purchase #7	$21.45	6.427%	$22.8286	$22.83	$22.85	$22.80
7 purchase totals =	$588.63		$642.2780	$642.28	$642.35	$642.20