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	$114.31	12.513%	$128.6136	$128.61	$128.60	$128.60
Purchase #2	$37.71	12.662%	$42.4848	$42.48	$42.50	$42.50
Purchase #3	$90.86	9.374%	$99.3772	$99.38	$99.40	$99.40
Purchase #4	$135.35	9.270%	$147.8969	$147.90	$147.90	$147.90
Purchase #5	$61.97	11.345%	$69.0005	$69.00	$69.00	$69.00
Purchase #6	$99.75	3.738%	$103.4787	$103.48	$103.50	$103.50
Purchase #7	$100.39	7.326%	$107.7446	$107.74	$107.75	$107.70
7 purchase totals =	$640.34		$698.5963	$698.59	$698.65	$698.60