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	$160.78	13.304%	$182.1702	$182.17	$182.15	$182.20
Purchase #2	$240.31	8.561%	$260.8829	$260.88	$260.90	$260.90
Purchase #3	$65.36	8.673%	$71.0287	$71.03	$71.05	$71.00
Purchase #4	$15.48	12.567%	$17.4254	$17.43	$17.45	$17.40
Purchase #5	$80.35	12.498%	$90.3921	$90.39	$90.40	$90.40
Purchase #6	$180.89	3.614%	$187.4274	$187.43	$187.45	$187.40
Purchase #7	$195.66	13.320%	$221.7219	$221.72	$221.70	$221.70
7 purchase totals =	$938.83		$1,031.0486	$1,031.05	$1,031.10	$1,031.00