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	$29.40	13.367%	$33.3299	$33.33	$33.35	$33.30
Purchase #2	$165.41	12.460%	$186.0201	$186.02	$186.00	$186.00
Purchase #3	$134.49	3.574%	$139.2967	$139.30	$139.30	$139.30
Purchase #4	$20.56	13.384%	$23.3118	$23.31	$23.30	$23.30
Purchase #5	$25.34	12.449%	$28.4946	$28.49	$28.50	$28.50
Purchase #6	$88.57	11.845%	$99.0611	$99.06	$99.05	$99.10
Purchase #7	$140.66	11.328%	$156.594	$156.59	$156.60	$156.60
7 purchase totals =	$604.43		$666.1082	$666.10	$666.10	$666.10