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	$136.94	13.354%	$155.227	$155.23	$155.25	$155.20
Purchase #2	$64.83	9.540%	$71.0148	$71.01	$71.00	$71.00
Purchase #3	$238.69	8.520%	$259.0264	$259.03	$259.05	$259.00
Purchase #4	$203.48	9.808%	$223.4373	$223.44	$223.45	$223.40
Purchase #5	$209.46	10.462%	$231.3737	$231.37	$231.35	$231.40
Purchase #6	$25.68	6.710%	$27.4031	$27.40	$27.40	$27.40
Purchase #7	$109.97	12.398%	$123.6041	$123.60	$123.60	$123.60
7 purchase totals =	$989.05		$1,091.0864	$1,091.08	$1,091.10	$1,091.00