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	$101.61	7.399%	$109.1281	$109.13	$109.15	$109.10
Purchase #2	$65.90	12.155%	$73.9101	$73.91	$73.90	$73.90
Purchase #3	$11.59	6.329%	$12.3235	$12.32	$12.30	$12.30
Purchase #4	$84.42	3.756%	$87.5908	$87.59	$87.60	$87.60
Purchase #5	$63.86	11.527%	$71.2211	$71.22	$71.20	$71.20
Purchase #6	$155.38	12.869%	$175.3759	$175.38	$175.40	$175.40
Purchase #7	$38.54	9.567%	$42.2271	$42.23	$42.25	$42.20
7 purchase totals =	$521.30		$571.7766	$571.78	$571.80	$571.70