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	$105.84	11.578%	$118.0942	$118.09	$118.10	$118.10
Purchase #2	$25.88	9.298%	$28.2863	$28.29	$28.30	$28.30
Purchase #3	$119.92	9.256%	$131.0198	$131.02	$131.00	$131.00
Purchase #4	$106.56	12.818%	$120.2189	$120.22	$120.20	$120.20
Purchase #5	$106.75	7.479%	$114.7338	$114.73	$114.75	$114.70
Purchase #6	$169.50	9.440%	$185.5008	$185.50	$185.50	$185.50
Purchase #7	$243.91	13.784%	$277.5306	$277.53	$277.55	$277.50
7 purchase totals =	$878.36		$975.3844	$975.38	$975.40	$975.30