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	$30.33	11.715%	$33.8832	$33.88	$33.90	$33.90
Purchase #2	$27.69	12.471%	$31.1432	$31.14	$31.15	$31.10
Purchase #3	$123.25	3.754%	$127.8768	$127.88	$127.90	$127.90
Purchase #4	$116.75	13.507%	$132.5194	$132.52	$132.50	$132.50
Purchase #5	$40.40	12.735%	$45.5449	$45.54	$45.55	$45.50
Purchase #6	$171.84	13.606%	$195.2206	$195.22	$195.20	$195.20
Purchase #7	$67.48	12.300%	$75.78	$75.78	$75.80	$75.80
7 purchase totals =	$577.74		$641.9681	$641.96	$642.00	$641.90