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	$73.31	12.498%	$82.4723	$82.47	$82.45	$82.50
Purchase #2	$86.43	4.646%	$90.4455	$90.45	$90.45	$90.40
Purchase #3	$50.65	12.775%	$57.1205	$57.12	$57.10	$57.10
Purchase #4	$120.50	9.488%	$131.933	$131.93	$131.95	$131.90
Purchase #5	$200.61	9.142%	$218.9498	$218.95	$218.95	$218.90
Purchase #6	$185.69	3.260%	$191.7435	$191.74	$191.75	$191.70
Purchase #7	$185.86	3.402%	$192.183	$192.18	$192.20	$192.20
7 purchase totals =	$903.05		$964.8476	$964.84	$964.85	$964.70