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	$89.85	11.568%	$100.2438	$100.24	$100.25	$100.20
Purchase #2	$215.41	7.365%	$231.2749	$231.27	$231.25	$231.30
Purchase #3	$201.33	12.427%	$226.3493	$226.35	$226.35	$226.30
Purchase #4	$246.82	11.751%	$275.8238	$275.82	$275.80	$275.80
Purchase #5	$38.66	12.529%	$43.5037	$43.50	$43.50	$43.50
Purchase #6	$27.85	9.818%	$30.5843	$30.58	$30.60	$30.60
Purchase #7	$18.25	13.719%	$20.7537	$20.75	$20.75	$20.80
7 purchase totals =	$838.17		$928.5335	$928.51	$928.50	$928.50