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	$137.61	3.607%	$142.5736	$142.57	$142.55	$142.60
Purchase #2	$176.52	7.582%	$189.9037	$189.90	$189.90	$189.90
Purchase #3	$166.44	7.205%	$178.432	$178.43	$178.45	$178.40
Purchase #4	$28.73	4.115%	$29.9122	$29.91	$29.90	$29.90
Purchase #5	$151.86	7.129%	$162.6861	$162.69	$162.70	$162.70
Purchase #6	$247.92	12.134%	$278.0026	$278.00	$278.00	$278.00
Purchase #7	$50.54	8.681%	$54.9274	$54.93	$54.95	$54.90
7 purchase totals =	$959.62		$1,036.4376	$1,036.43	$1,036.45	$1,036.40